How can you stop male cats from spraying around your front door of your home?

This is an act of defining his territory , you might want to check if there are any male or female cats wondering outside the house , their presence might be the cause. Also I read from somewhere that when neutering wasn't performed satisfactorily, they may still retain the trait of unneutered (same with spaying). If there are some tissues left over or something, that can cause them act as if they aren't neutered. But most likely the cat's feeling some outdoor cat around the house and being defensive.