A message on the front of the manual for BlueAnt's Pump HD Sportsbuds wireless Bluetooth headphones reads: "The best possible sound comes from the best possible fit."
With bona fide in-ear headphones like the Pump, that's true, because if you don't get a tight seal you lose a lot of bass. To help you get that tight seal, BlueAnt includes a couple of optional stabilizers that snap onto the buds. Ostensibly, the stabilizers are there to help "lock the Pump in place" when doing more extreme activities, but I couldn't get a tight seal without using them.
The stabilizer design works well overall, and these headphones really stay in your ears (they didn't move around at all when I used them on a treadmill and elliptical machine in the gym) and should provide a comfortable, secure fit for most people, which is the most important when it comes to wireless sports headphones.
That said, I did find that at times that the stabilizer dug into my ear a little, and it would have been nice if BlueAnt offered different sizes of stabilizers and perhaps made them out of slightly less rigid rubber. If you're lucky, you won't encounter this issue, and some people will be able to get a tight seal and secure fit without using the stabilizers.
The headphones do seem durable and are waterproof. In fact, if you have all the ports closed off -- a rubber gasket covers the Micro-USB charging port -- you can literally put them under the faucet and rinse them off.
While Bluetooth doesn't transmit underwater, the other thing you could do is wear these in the pool if you keep your head above water. They have up to a 100-foot range, which is more than the typical 30 feet that Bluetooth offers, and battery life is decent enough at around 8 hours.