There may be some special home brew but more than likely it would wash
away as well.

I have heard of success with a big rubber or inflatable snake. A motion
detector that turns on lights seems like it would work, though I don't
know how expensive that would be and the deer might get used to it.
Maybe play a tape of coyotes howling? It shouldn't be too expensive and
wouldn't have to be too loud, I wouldn't think. Then there's an electric
fence?

Alternatively, You could plant something they like better away from your
trees and plants. Maybe they'll fill up before they get to the trees.
Some kind of grass, oats, clover. Then again, this method might attract
more deer.

Alan