Knee Dislocates during Aqua Run?

My knee has been dislocating when I take Aqua Run cles. (Aqua Run is jogging/running in a swimming pool with a belt on.) I went to the doctor and he did x-rays - everything looks fine. He is currently sending me for physical therapy, and my PT is having me do strenghtening exercises. My knee still keeps dislocating during cl. I have been doing this cl for 7 years - I have no idea why this is starting to happen now. If anything, I am in much better shape. My PT says I am hypermobile (too flexible) and I may have some muscle imbalances (hence the exercises). Does anyone know how I can prevent my knee from dislocating? Also does anyone know of a waterproof patella stabilizing brace that I can wear into the pool? I have tried to wear one that wasn't waterproof, but when it gets wet, it looses its effectiveness and offers no support. Thank you very much.