Two suggestions:
1) Return the favor by urinating on the owners whilst the dogs are marking their territory. This requires you to be fast on the draw, and willing to take a few punches.
2) Alternatively, purchase a portable air horn (like those used on small boats). Next time you catch a dog mid-stream, charge out blasting the air horn. This will scare the living ***** out of the dog, who will probably never mark your bike again.
I can't vouch for the effectiveness of #1 (never having tried this myself), but #2 works well for driving off stray dogs and black bears. Of couse, I doubt you have a problem with black bears marking their territory on your bike or cover...
