I asked a similer question about ants and was looking for companion plants, I had a reply to say mint seemed to work, so I was working on the theory it couldn't do much harm, so far it seems to have worked.
A word of warning though if you do go down this route, mint goes ballistic if it's not kept in a pot, I had a friend who just left hers and it took over the whole garden.... it did smell fantastic when she cut the grass though!