Anyone any advise, My Rottie has this obsession with Cats

He has made it is life's priority to attack, Chase, Bark, Drag Owner Along at the first sight of a cat.

I need help on this one any ideas??? I tried treats as a distraction but doesnt work for long enough, try's to get the treat then back on to the cat

Once they are obssessed like that its very hard to change them.
I would try walking him in something like a Canny Collar which will give you a lot more control, and keep him focused on working with you - than staring around him.
Plus, keep him on a lead at all times, as once they get this focused - odds are he will kill one if he catches it.

Dogmatic, Canac Gentle Leader, Halti head harnesses are probably best, depending on your preference. I prefer the Dogmatic - good strong construction and will stand up to a heavy set dog. Body harnesses are an acquired taste and if you have a dog that insists on pulling, the body harness does very little to control this. We have a doberman and she is like robodog once she decides she wants to go in a particular direction or a faster speed, so we use the Dogmatic head harness (or the padded halti). The Gentle Leader we bought fell to bits shortly after we put it on her.

Im going to try a canny collar, anyone know of anywhere local to buy one?

Pets at Home. Jolleyes, most pet shops have them. You'll probably need an XL one - but check what it says on the packet- usually, they give examples of the breeds of dog each size is suitable for. I think you'll be better with a head harness because it gives much more control than a body harness. I found the body harnesses we bought never stopped Ailsa from lunging - and when you're walking on a busy street, you dont want your dog to suddenly lunge into the path of a car because he or she has spotted a cat!

Oh- if you go to Pets at Home or Jolleyes you can take your dog into the store and ask the sales staff to help you to find the right size to buy. Good luck xK