I had a duck issue for 2 years, there were 3 ducks who were determined my pool was a play area and bathroom.

I tried everything I could think of... If I chased them off they would just circle until I went back inside then come right back! Worst of all, my dog didn't care about them, he would just watch.

I finally found a solution that worked... A high power green laser pointer (75mw), the point is extremely bright in the sunshine and you can see the beam as it goes through the water. I'm not sure if they thought it was a snake (that would even chase them as they flew away in an evasive pattern).
They tried alterting the time of day they would come, but after it chased them 3 times they have not returned... But I noticed 2 of them moved over acouple houses to their pool.

Might not be the perfect solution, as these high powered lasers are expensive and can be dangerous, but it did work for me!