Lab/pointer cross sometimes agressive with other dogs?

[HotchpotchHoney]

especially if they are on leads?

drving me to despair, despite having a good recall and for the vast majority of the time is far more interested in his ball then anything else around him. Very occassioanaly he will growl and become agressive with other dogs.
it happened on our walk yesterday, walking two dogs nicely by the river they were off thier leads, we managed to lose his ball, but carried on walking and he was just running around.
another dog was coming towards us and on a lead, as a courtesy i always put my dogs on a lead if approaching someone with thier dog on a lead. my partner call him to him, he came over and just as my partner opened the clip to put the lead on he made a bolt for it and was growling and barking at this other dog.
Quite frankly its embarrasing and a poor show. Hes a very active labrador/pointer cross and so needs extensive off lead walks and ball chucking to tire him out and exercise him enough.

We got him from a rescue centre as a puppy and hes now approaching two years old. This is a relatively new thing and i can;t find advice anywhere on what to do?

the children and i would be devastated to let him go

[fruitshootsandheaves]

Dogs are often more aggressive on lead as they feel they can't get away from a situation.
You need to try to get him to associate nice things when other dogs are near, call him back and give him a treat or his ball, if you do this enough he should learn to come for his reward when he sees another dog.
It sounds easy but I can sympathise with you, I have a collie and she is not generally very good with other dogs, however she will stop as soon as she sees another dog and come back now, but she does not like it if they continue to come up to her. If I know a dog is coming and I can't prevent it I put her in a down and wait for it to go away before walking on.
HTH

[HotchpotchHoney]

thank you. will try that, back to pockets full of kibble :o

our cairn terrier will run up and play with other dogs and not be bothered by them but if the lab starts barking she will join in.