I work as an installer for these type of systems, as well as security and home theater. The volume controls are convenient to have, and I wouldn't shy away from them over concerns about degradation in sound quality. Just be sure to get one designed for outdoor use and put it in a gasket sealed housing. Same goes with the wire and any necessary crimp caps - use the weatherproof stuff.
Also, various animals find certain brands of speakers delicious. I can't say why, but I know that squirrels and deer seem to prefer outdoor speakers from Mirage over most "rock" speakers. They can really do some damage, so be prepared.
Also, various animals find certain brands of speakers delicious. I can't say why, but I know that squirrels and deer seem to prefer outdoor speakers from Mirage over most "rock" speakers. They can really do some damage, so be prepared.