cat hunting

So we are still having SERIOUS problems with Leroy and his cat obsession, inc having a slight incident where he caught a neighbours cat - he was sniffing down the bottom of a bushy tree he likes to do his business in, all of a sudden darted into the bush an came out with a cat in his mouth - lying sideways hiss and clawing a lot, managed to give him a good shout and hard tug on the lead an luckily he let go and the cat bolted away. This is the second time he has done this, the first time was with my mother-in-laws 19yr old cat (she is literally bone and fur very old and tiny) he chased her into the house at a family BBQ and managed to get a hold of her and my m/i/l had to grab Leroy and luckily get the cat out his mouth - by which time Diesel had come to have a look as had my m/i/l dog Skye and my ohs aunts 9month old pup, but good on the cat she was sitting in the middle of the kitchen trying to take all 4 dogs on!!   i was suprised she survived the attack, but now that Leroy has attacked a cat in the street this behaviour really cant go on!
I am at a lose of what to do, from the min we leave the close for our walks he is in hunting mode, his ears are pricked up, his nose is going mental, his eyes are darting about and he is either chest up pulling like mad or his nose is stuck to the ground following trails of the smell of cats. He knows every window that cats sit on in my street (inside flat cats) he is like a dog possessed!! I've tried taking out squeaky toys to distract him, didnt work, tried focus training, he will sit look at you i keep his look til hes not looking between me and everything round about him and then give him the treat, but then he just goes straight back to hunt mode! an i now feel like i'm almost rewarding his hunting mindset and not his calm mind set!

When we first rescued Leroy he was great, Diesel and him used to walk side by side and it was really nice, they could both pull on occasion but nothing i couldnt fix, now Diesel (who is soon to b 2 is calming down a lot now) walks virtually by my side and if she does pull all i need to do it stop walking and shel return to my side and walk fine again and Leroy is out in front pulling about here there and everywhere!
I've tried the stop/start technique (which worked with Diesel) Leroy will stop, eventually turn round come back towards me but the min i move he jolts to the end of the lead, so it just ends up in a "stop-jolt-stop-jolt-stop-jolt" and we dont get anywhere. I also previously tried the turning in a different direction technique but that didnt work either (took me and hr to walk a 5min walk and still wasnt sink in to him)

If i was to get a halti or canny collar would that help me to control his head and therefore keep him focused more on the walk and less on whats going on? and also stop him from walking with his nose stuck to the ground?

I know his hatred of cats is something that is clearly just in him, but surely i can learn ways to control it or make it more manageable? As it stands he no longer gets off lead in case a cat appears and he does a bunk, which is a shame for him, but also for Diesel coz she misses playing with him. Since he caught the cat i've also thought that i would maybe need to start musseling him to stop him from eating another cats hiding that i dont see?
I know i good "leave" would also help, so when he does walk on i give him lots of praise and treats. Someone had suggested getting a toy/stuffed cat and training him to leave that....but i dunno if i dog would make the association between a toy cat and a real cat? Although was thinking i could maybe get my friend who has 2 cats to keep the toy in her house for a while and maybe rub it on her cats so the toy would get the scent of the cats on it? or is that just silly?

If it's a case of trying anything you can then no I don't think it's silly. This isn't a problem I have so I'm afraid I don't really have any advise to offer. However, personally I wouldn't muzzle him because of this, just keep him on the lead. Get a long training line and then he can still have his play time with Diesel. Hopefully someone will be along soon with experience of this to help you more  

glad to see you don't think its a totally silly idea, i have seen cat toys that move and "purr" and thought that this would be good coz could train him against the movement too. I had considered getting a real cat - one that was calm and didnt mind dogs, keeping Leroy on his harness and lead for control and training him to leave, and rewarding him for ignoring it but i just thought a toy would b a lot safer.

Just out of interest is it just cats or does he just have a high prey drive with any small furies, birds etc?

nah its just cats, birds squirrels and rabbits will maybe grab his attention when they move but he just looks and then continues on his way.

Diesel has quite a big prey drive, she's easily distracted by small furries and needs a good "leave" to continue on her way - but funnily enough doesnt bother with cats lol Leroy's thing with cats is beyond prey drive and like i said no other small furries really phase him

I would be interested in the responses here as ozz has a massive prey drive for anything that moves

Dempsey hates cats with a vengeance! If you find something that works (a toy won't, cause he'd just rip it to pieces & he'd know it wsn't the real thing anyway) let me know!