We made a small design mistake when we were installing our spa. It has a knife-edge border between the spa and the pool. It's like the Riviera for neighborhood doves, who like to dip stale bread in our water and poop on the tile.
1st Solution: Scary Fake Owl
Naturally, I wanted to prevent doves pooping in my pool. So I got this scary fake owl.
It didn't even work a little bit. If the doves noticed it all, it just helped them relax and move their bowels more freely.
2nd Solution: Scary Real Dog
When we were having some plumbing work done inside and outside our house at the same time, I parked a 90 pound dog inside the pool fence. I figured she would scare the doves away for at least a little while.
It didn't even work a little bit. She slept calmly in the shade and the doves seemed glad for the company.
3rd solution: A Slingshot
I went on eBay and bought a "hunting slingshot." The slingshot is plenty powerful to destroy a dove, but there are 2 problems with that: 1) a missed shot would probably break a pool tile and 2) cleaning up dove carcasses is not much better than cleaning up dove poop.
So I got really light-weight ammo: Airsoft BBs weigh in at a fifth of a gram and they can't really do much damage. I also have some practice ammo. They're also lightweight and mostly harmless, but they bounce really far when they hit a hard surface.
This actually worked well. You don't even have to hit a dove. If a fast-moving projectile hits anywhere near one of them, they all fly off in a rush.
2nd Problem: Doves are quite stupid
It turns out you can hit doves with airsoft bbs over and over and over again, and they keep coming back. They just land on a power line above the alley and wait a minute. Then they all descend on the pool again.
I deem this problem unsolvable.