Thanks for your wildlife-friendly response, RG. As I've said before, I hate to see things killed just because they're going about their normal existence in a way that we find inconvienient. Skunks are a good hunters of grubs, but I understand that they're not something that you want in close proximity to your home.
First, make sure that there are no food sources around that might be attracting them. (garbage cans, pet food, open compost heaps, etc.)
Skunks are, oddly, sensitive to strong smells. The moth ball thing could work, but they contain some pretty noxious stuff. If you go that route, put them in a jar with holes in the lid to keep them safe. This also works with rags sprinkled with ammonia. Again, keep it in a jar. If you can find the skunks burrow, place these in or near the entrance.
Trapping can be dangerous and is often only legally allowed by professionals. Use good judgement. Skunk spray can be VERY difficult to remove if you get sprayed.
Cayenne pepper has worked for me, but has to be re-applied on a very regular basis. I've also had limited success with fox urine.
Really the most fool-proof is some type of barrier fencing. Once they are deprived of a food source, they'll normally go on their way.
Not for everyone, but having a dog around works wonders.