Same here,gravel road and three dogs that shed all summer. I keep them covered with squares of fabric and vacuum the speakers. There are custom covers you can buy also.There's one or two companies that come up if you Google it.
Dust Removal
We live on a dirt road and thanks to certain neighbors who refuse to slow down, we are constantly wiping dust off horizontal surfaces in our house. I'm sure there must be dust inside my components but am not sure of the best way to deal with it.
Blow it out w/ compressed air?
Use a vacuum?