Deer whistle or coyote pee to deter deer

Hi, I was just wondering whether anyone here has thought about trying a motion detector that would set off a deer whistle to keep deer away from gardens or trees. Would this just be another stimulant they would get used to?

Also, does the coyote pee thing actually work? And wouldn't it end up attracting coyotes as well as deterring deer?

I have only tried a motion detector sprinkler, which has been VERY helpful with keeping deer and rabbits away from new tree seedlings and saplings. I use the Scarecrow and change the direction every 3-4 days.