I would advise having full thyroid check if you haven't had it done.

My 10 year old was becoming more and more aggressive and grumpy to me and my other dog. Once tested he was found to be hypothyroid with virtually non existent levels. It's taken a while but with medication he's much happier and less aggressive

What exactly did the vet do to declare 'perfect health'? What kind of tests etc?

I don't think aggressive behaviour could come from simply being spoilt. Most aggressive behaviour develops out of fear, stress or medical problems.
A dog won't simply become aggressive towards you because you start implying rules.. this sounds like 'pack leader/dominance theory' advice to me.
Start thinking what has changed in your life recently, in which situations is he showing aggression.
Btw I completely agree with Mattie, growling isn't aggression as such, it's a warning sign that you need to take seriously. But instead of telling the dog to stop growling, you need to find out exactly what triggers it. Growling usually shows us the dog isn't comfortable with a situation. Could be pain, could be stress, raised testosterone, thyroid underfunction etc.

Look at the general body language of your dog, is he relaxed? Does he show a lot of stress signs? Is he suddenly hyperactive?

I must admit that when I saw your response I agree with what Mattie has written.

It sounds to me like your Vet is of the old, outdated, cruel and pretty much useless "dominance" theory, the idea that dogs should be lower do the pack etc...

Do you teach your dog commands? Does he know sit, down, stay etc... I think it's good for your dog to know you expect certain behaviour from him, I don't think it is useful to think you've spoiled him! I spoil my dog rotten - he gets away with far more than he should, but when I go into training mode then he does too.

He did, but he checked for parasites, not thyroideal problems.

It's usually when you don't allow him to do something. The first time he growled and try to bit me was because we were in the garage and he wanted to go behind the car and I didn't let him. First I stood blocking the way and he was fine, but then I moved, he waited till I was in the door and tried again, so this time I pulled him by the harness (not even hard, just to stop him) and he tried to bite me (I pulled my hand just on time).

The second time around, we were playing with Zeus (a puppy) very normally since they do get along. But all of the sudden they wanted to come inside and I couldn't let them because they had stepped on poop and I wash their paws first. So they rush in and I blocked the way, again, standing up. They insisted and I shoved them both (at the same time, they're not so big) but not hard, just to push them out. Zeus understood and went out to try and keep playing, but Estambres (the aggressive one) followed him and started to growl at him and to try and mount him from the front. Zeus got scared as Estambres was even trying to bite him, Estambres got one of Zeu's legs and so I ran to hold Zeus in my arms. This time I didn't touch Estambres at all, I was just picking up Zeus because he's a puppy and he was in disadvantage. The minute I picked Zeus up, Estambres came growling and, this time, he did bite my hand.

I take my dogs to a teaching hospital in hopes that they get better treatment, since they have the attention of one teacher and three to four students. But I guess the teacher most be outdated

He does follow the basics. He sits and he jumps when told to. I didn't try to tell him to sit when he was attacking Zeus, so maybe it was my mistake that way. Since I didn't nag him or anything (I just picked Zeus in my arms) I wasn't expecting any aggression and I didn't know how to handle it.

Firstly I would suggest not to man handle him. Dillon my Bernese not an aggressive bone in his body see's it as a challenge if you try to stop him from doing something and try to move him admitted he is younger than your dog but most dogs do not like being yanked even if gently it is not that they are being dominant they are asking you not to do it.
Try having treats in your pocket and use them as a lure and when he does what you have asked reward him.
Thyroid panel still might be worth looking into as others have said. I would be concerned if my once obedient good tempered dog suddenly changed behaviour wise.

I think I'll ask to get it done, thank you
They did a physical check up, the usual: they put them in the balance, they measured his size, his heart rate, his blood pressure. And they did get blood analysis but they were for parasites and "infectious diseases".

The growling comes when you don't let him go somewhere he's not supposed to, I guess. If you just block the way, he's fine, but the instant your reach for him, he bites.

Maybe this is the problem. I had other dogs who reacted just fine if I moved them, including Zeus, the dobie I have now. Since I wasn't doing it in a rush or violent manner, I didn't think he'd be challenged by it! But thank you very much for letting me know that.

I'll try with the treats and the blocking paths he's not supposed to take instead

I would get him checked for thyroid problems, even if there isn't any it will give you peace of mind and help you with his training.

Does he wear the harness all the time? In order to get hold of the harness you would have to go either over his head and neck or close to it, to a dog that is aggression and many dogs will bite. To stop a dog going were I don't want him to once I have blocked his way I encourage him to do something else, either go a different way or a little training, sit, down etc, only one or 2 times to get his mind away from what he was doing.


Dogs push each other so really there shouldn't be a reaction to the pushing, again what may help is giving them something to do like sit or down. This should distract your dogs enough for you to be able to wash their paws.

I do find giving dogs something to do in these situations helps a lot, it distracts them away from what they were doing and give us time to take control.

I don't use treats in these situations because I don't want to have to carry treats round with me all the time, dogs come to expect them and if you don't have any they are disappointed and remember the next time that they didn't get a treat. It isn't wrong, just that I prefer to distract by giving them something to do and not to eat.

He doesn't wear the harness all the time, I only put it on when I'm gonna walk him or when my dad comes home (to hold him so that he doesn't go out when he opens the main gate). My dad had arrived and he had just parked, when the dog tried to go to the other side of the car I held him back, but I reached him with my hand from behind, so my hand was never over his head/face. He turned and bite me when I stopped him from going there. I can't block that path permanently because it's a little space that my dad needs to have to walk from the driver's side to the house. At first I stood there and blocked him, I distracted him with bubbles and we were fine. But I turned around a second and he was trying again, and that's when the incident happened.

I already made an appointment to the vet for next week (that's the closest they had) and he will get the tests

Thanks for the advice on distracting him, I didn't really think of giving the commands he knows to make him focus on something else