Not completely, no. People are always going to improve their way of hacking and stealing. Good news though - if you make it inconvenient for them they're more likely to move on to another easier-to-steal game instead. Unless they really want your game for some reason in which case, no. It's not possible if they're 100% prepared to go all the way.
After all, look at all the AAA games that get leaked and pirated. They have infinitely more money to pour into protection than indie game devs do. Thankfully, indie devs are less likely to be targetted than big name games, so that does afford you some protection, minor though it may be.
As for those asshats who go out and steal others' work to claim as their own, making your game harder to crack is going to deter them more often than not. Usually they're after a quick and easy steal, so if there's some kind of protection that they can't easily get past then they're likely to just move to another game instead.
Unless they're obsessed on your game (which I have seen happen before >.<; ) in which case, slapping your name all over the social media and letting it be known loud and proud that it's your game, with date stamps and such, is the best protection from that type of jerk. They can't claim your stuff if everyone knows it's not theirs, after all.
