Are intrinsic monopolies inherently non-libertarian?

There exists certain sectors of the market that, by their very nature, end up becoming monopolies, and, therefore, anti-competitive. The most obvious example of this would be utilities (think power distribution (even the poles themselves), water mains, sewage, etc). Is there any way to combat these sorts of monopolies with the existing system, or would a new system have to be devised using decentralized alternatives?