How do I keep yellow jackets out of my pool?

We had an exterminator come out a couple of days ago. He told us he could get rid of them, but after we'd paid him and he sprayed, he revealed that he could get rid of everything but. That jerk almost missed the tiny nest in our roof near the pool. He knocked it down, taking out a few baby YJ's with it. We thought we were in the clear because we hadn't seen any. Today I tried to go swimming and two came out. (There used to be 3-4 so I guess that's an improvement). In an act of desperation, I grabbed a bottle of Fry's brand mouthwash and flung 3/4 of it in to the pool. The exterminator suggested I try Lysterine but we were out. Of the two YJ's, one flew away and the other attacked. Anyone within a mile radius heard me scream, but I'm not stung. So far, the pool is clear, but I'm too frazzled to try swimming again. Please help. I'm afraid of anything that flies and is smaller than a plane.