How do I keep frogs away from (and out of) my outdoor spa?

I hope I posted this question in the right catagory.

During the summer when it starts getting real dry, frogs seem to home in on the water vapor from my spa. When I open the cover, there will be several of the little critters sitting in there enjoying themselves. I remove them from the spa but others show up later to take their places. To begin with, it's kind of hard to keep the ph of the water regulated and keep it sanitized using bromine and the frogs aren't helping me any by being in there. Is there any product available that I could use that would repel the frogs and keep them away? I saw a program on TV once where a married couple who lived in Hawaii had a similar problem. They didn't have a spa but their property was being overrun by African frogs that were accidently introduced into the eco system there. They didn't like the frogs because they were extremely noisy at night. These people sprayed citric acid around their property which would keep the frogs away for a while but they kept having to respray all the time. What I'm afraid of is that one might die in there and cause me more water problems. Anybody got any suggestions of how to keep them away?