I had my leafeon neutered a month ago to stop him wandering which he did a lot but when we go out he still tries to looks for females to mate with. Is this normal behaviour that he will continue?

Unfortunately, while there’s a strong chance that neutering your pokémon will calm him down and stem some of his more aggressive behaviors, it’s never a guarantee. There are certainly cases in which pokémon are just as aggressive about finding a partner after neutering as they are before, and yes, it’s technically normal behavior (in that you shouldn’t worry that anything is wrong with your leafeon).

On the positive side, neutering also prevents certain health problems in leafeon, besides the obvious fact that your leafeon can no longer produce offspring. That is to say, if he does get away, there will be less of a chance that he’ll come back to you with eevee pups or, well, something worse. At this point, I would recommend implementing some alternative ways to keep him at home, namely fences and a bit more rigorous training. Consider getting him a spayed female partner at home as well to encourage him to stay, rather than wander off and potentially quarrel with wild or neighboring males.