Not much of an issue in the ocean, but in a local lake with lots of boat traffic, this isn't such a great idea... (in reference to tag line)
My main concern on Lake Pleasant, or any other lake in Arizona, for that matter, would be theft. I've had stupid, drunk people on jet skis decide to use my dive flag as a reference point for donuts at Lake Pleasant. I've also had stupid boaters come right up to my dive flag at Canyon lake and pick it up out of the water. This was with shore support yelling at them to get away from the flag. I could easily see lots of people coming up to an unattended boat on the lake and even taking it for a joy ride. Again, I'd also check with the lake patrol about unattended vessels. You could get cited for it.