We have an 7 year old miniature foxie x chichuaha, male. We bought him as a pup and he was a lovely pup, he was socialised with dogs, cats and other farm animals from an early age and he was also socialised with other people. The older he got the more his personality "set in" he began to nip and the back legs of the horses if he thought they were in his territory which doesn't end up going very well (three vet trips for being kicked), thankfully he seems to have learned from those experiences and no longer does that.

However, he is very aggressive with our other dog, the dog which he was brought up with has since passed and we got this new dog as a pup too, she is a lovely obedient lady who is really still a pup and submits to his growls even though she's four to five times his size. He will attack her for no reason, when they are playing with a ball he'll suddenly turn and bite her and hes even drawn blood in his savage little rants at her.

He has to be locked in a room if we get visitors with small children as he runs out and bites them. We have two children who are both gentle with the dogs, I don't allow the youngest to have any unsupervised access to the little dog even though the dog wags his tail and licks him if he corners the dog or tries to pick him up the dog will bite. He is extremely territorial now and his aggression towards people and the other dog is getting out of hand. He is reasonably obedient when he wants to be ie he'll come back when called if chasing something and he sits, stays etc too except when a car pulls up and people get out.

Now, I've tried putting him in a room and then letting him out, I've tried leaving him in the room the whole time, I've tried putting him outside when he's bitten someone inside and vice versa, I've tried squirting him with water and yes I admit I have also given him a smack.

I know someone else who got a pup from the same litter and it was worse as far as aggression towards people go and it was socialised well early on too.

I guess I'd like to know why he's progressively gone this way he's never bitten me at all but he does with everyone else, he constantly growls at the other dog and is completely un trustworthy with the children and visitors. Is there anything I can do at this late stage or do I just stick it out?

The pup is off to the vet for desexing should I send the small man too or is it too late (hormone wise) to make a difference?