The only bad experience I've had with a dog was when my girlfriend's pug decided to pee in my guitar case. Fortunately, the guitar was not in it!

Btw, don't go bad-mouthing cats -- if you're living on a farm or in the country, you'll find they do a lot of good in the way of pest control. I'd much rather have a cat or two than to go leaving poison or traps about.