I've used dunks but not with my ducks water. I dump it out every night and fill the kennel one before I put them in at night. In the morning I dump the kennel one out and set it in the sun to dry and air out the kennel. I have the water tub siting on top of boards so air can get under it. Where I dump the "outside" water the evening sun is shining there so I give the ducks a little time to graze before I put them in. I use my dog's pool water to water the trees. I don't blame you though, I HATE mosquitoes! There's a spray I used last year just around the yard called Cutters and I know there are some organic yard/air sprays that are supposed to work for 8 hours. I didn't have ducks last year but I could spray and not worry about my dog or my grandkids being outside after I sprayed. I've tried herbs but this year it's so dry here that I'm losing most of my garden...I have things eating my basil and my dill even...it's just horrible! I even planted mint around my ducks' kennel and that's not keeping them mice away...thinking of getting a kitten and just letting it live with my ducks.