Do I need my aggressive, biting ****zu castrated?

Charlie, is an entire male Shihtzu who will be 3 in September. He has always had a lovely, playful, spirited nature and coped well with plentiful attention from both adults and children of all ages.
Following a recent split with my partner, myself and Charlie have moved into my parents house - somewhere he is familiar with as he spent most of the day here when I was in work and not living with them!
On a few previous occasions - literally no more than 4 or 5, Charlie had growled at my ex partner when he felt he had displayed threatening behaviour, such as leaning over him, reprimanding him etc. However, since we have moved into my parents this behaviour has got seriously worse.
Training classes mean he responds to simple commands such as sit, down and stay when he wants to, and we have also seen a behaviourist but have made very little progress.
Within the last 4 weeks he has bitten both my dad and my mum in two separate, completely unprovoked situations - my dad leant over to open the patio door, my mum leant around the wall to see if I was asleep!!
Please help - ANY suggestions would be welcomed, I am seriously considering castration, or even worse as I can no longer trust Charlie around adults and especially children!
Please Please help!! Thanks xx

The aggressive behavior might be mitigated if you get him neutered but don't expect a quick fix. You also have to put forth on your part with training. But yes, this would be a good start.

Next, it could be that your parents need to start forging a strong bond with the pooch. To do this they must take part in walking him, playing with him and training him. I would try hand feeding for a while. Withhold his daily meals, measure out how much he gets daily and give it to him as rewards (3-4 kibbles at a time) during training. Have your parents also do this. If the behavior gets better then you can go back to giving him his meals in his bowl.

Some good guidelines to follow are the NILIF:

Byrnes, Carol A. Follow the Leader!< http://www.diamondsintheruff.com/leader.html >

Byrnes, Carol A. Should You Sleep With Your Dog?< http://www.diamondsintheruff.com/dogsinbed.html >

Byrnes, Carol A. Work to Earn.< http://www.diamondsintheruff.com/foods&feeding.html >

McKean, Deb. Nothing in Life is Free.< http://www.k9deb.com/nilif.htm >

Milani, Myrna. Leadership vs. Dominance: Who Leads Your Human-Canine Pack?< http://www.mmilani.com/leadership-vs-dominance.html >

Ryan, Kelly. Are you Alpha?< http://www.4pawsu.com/leaderadv.htm >

Ryan, Kelly. The Serene Homecoming.< http://www.4pawsu.com/Serene.htm >

You may think Charlie is settled but from the sounds of his behaviour he isn't and is finding the extra people in the house and his new situation a bit stressful.
I wouldn't consider neutering at this moment as it will only work if the behaviour is motivated by testosterone and in some instances can make the matter worse.
First would be to try and tackle the problem.
Now you say both occasions were 'unprovoked' but from the forst with your dad, did your dad lean over the dog? That is quite an intimidating event for a small dog and you have already said he has growled at your ex when he leant over him. The second your mum leant round the wall, again that can be quite intimidating for a small dog for a big human to suddenly loom into view.
You need to make Charlie feel a lot more comfortable and confident in this new situation, it will be hard as you yourself will be quite stressed with recent events and dogs can pick up on the slightest things, that even we may not be aware of, and react accordingly.
Becky

Castration takes up to 6 months to take effect, and will only affect testosterone-fuelled behaviour. From what you say, the dog is reacting from stress, not anger.
I`d be trying to de-stress the dog by giving him his own safe space - bed, blanket or (open) crate where he is not disturbed. You could also try a DAP diffuser as I found this helped with a new foster.
Ignoring the dog might also help. This takes the pressure off the dog and also gives him an incentive to please you - to get attention / reassurance.

Hi! Thank you for your quick replies!! My mum and dad already have a lot to do with him, they also feed, walk and play with him and Charlie does respond to the commands when they say them!! I will try the holding back of his meals though, thank you for that!!

I'm going to take him to the vet for some more advice, they've said they'll check him over to ensure its not a medical reason - but at this moment I think I'm definitely going to opt for castration after a lot of research!!

Sorry, what is a DAP diffuser?

is he protective of you?

have you bought him up to be pretty much coddled to you, ie, lots of carrying around, cuddles on your lap, so on so forth?

as the others have said I dont think castration is the best answer here
Sounds like a insecure unsettled wee dog who

keep going with training classes cos training tricks and things can help build your dogs confidence

If you are not happy with the behaviourist then see another one - there are lots out there and not all as good as they should be

and for the moment be careful not to startle or threaten him

I would also get his eyes checked