My dog doesn't like unneutered males...

Has anyone else got a dog who hates uncastrated males? Henry really dislikes them, especially if they bound up and try and sniff him.. he really growls and chases them off in no uncertain terms. It only seems to be uncastrated males, especially younger ones.

Shamus is anxious about entire males. It is quite common.
Work on your recall and call him back to you when you see one?

I don't think you should expect your dog to get on with every single other dog it meets - it's quite an unnatural expectation of most animals really.
I would do as suggested, work on getting a solid recall around dogs and teach your dog to ignore other dogs or focus on you. Training for a "watch me" command could be useful. Your dog doesn't need to play with every dog it sees but when you know there's a potential issue, you do need to ensure you can control your dog enough to call it back and pass by the other dog without anything happening - if you can't do that then you need to physically restrain your dog with a lead or longline when you can't predict coming across unneutered males.
I would say that mostly it's the other owners at fault for letting their dog bound up to yours without checking if it's OK, but sadly life isn't always fair so much better to be the responsible owner who can call her dog back and carry on with your walk peacefully - if only for your own benefit and that of your dog's wellbeing.

Thanks both of you - good advice.

Usually we do call Henry over if we're not sure of the dog or go the other way, but today we were in the woods and the dog just appeared out of no-where and the owner was quite a way behind, so we couldn't really avoid the dog and it came straight up to Henry... Am I being too hard on him? I came home feeling quite negative about him, which I don't do normally as he is such a lovely dog.

I think you should be proud of him. These strange dogs are rushing up invading his personal space and he is doing a very natural, restrained reaction by growling (growling is GREAT - it's a natural warning, showing lots of restraint by giving this warning, not just a bite) and chasing the dog off but coming back to you when it goes away. He is reacting far better than a dog who may just stand his ground and start a fight, or one who chases the dog until he catches it and has a go at it physically.
Society seems to suggest that we should all be able to trot down to the park and have all our dogs of all different ages, breeds, genders, etc. all getting along like best buddies. This is so not the case, you cannot make your dog like every single dog, even if you socialised him as much as physically possible, he could still take a dislike to a dog for its body language, its scent - all sorts of things you can't control. All you can do is ensure that you can still retain an element of control in this situation and recall him and put him on lead if necessary, that is the best you can do and more than adequate IMO. If someone lets their dog run over and lacks that control to call their dog despite you making the effort to recall theirs, then it's their problem - but they should be grateful that all he will do is give the dog a telling off. Their dog may sadly approach a dog with a lot less restraint one day and they may come off a lot worse.

Thanks very much for that - it's really made me feel better. Henry never goes in and makes the "first move" when this happens - it's always when the dog approaches him, so when you put it like that, he's obviously not comfortable and makes his feelings known. It does sound very noisy, though! Also, it makes me a bit on edge on walks in case any unneutered males crop up around corners! Thanks again!