How can i get my dog to stop chasing cats and walk nice on his lead?

i walk my 11 month old french mastiff off the lead now his amazing. all i did was watch dog wisper and they teach you how to walk them in almost every episode when you walk with your dog of course on the lead make him walk beside you or a little behind you if he walks a little faster and looses his way tell him stop in a firm voice and snap your finger to the position you want him to return to it takes alot of time but you have to continue doing this for several weeks i hope it works for you