Don't know about getting $2 back at the front lockers. From my experiences, you don't have a key, it's done with a 4 digit password on a touch screen.
The lockers at the front of the park are the best idea if you're doing the water rides. Costs $5, located to the left as you walk thru the main gate. Bring a change of cloths, including shoes and socks.
What everyone else said is true.
Dudley - The front of your shirt will be wet, but will dry off after walking around for a few minutes.
JP - Not bad, a little splash on your shirt, no big deal.
Popeye - Will soak you. It is your shoes that you're trying to keep dry. I keep my feet lifted up. On a few drops, the entire thing fills up with a foot of water. You'll most likely get nailed from the people up above. I have managed to make it thru the ride without getting nailed by a water fall, but it was luck. When you pass under a water fall, it's like taking a shower. Your shirt will eventually dry off, but if your shoes get wet, they stay water logged. You must have shoes to ride. Sometimes they let people put their shoes in the middle compartment. If they make you wear your shoes, then I take off my socks and put them in the middle.
Don't wear flip flops, bring an old pair of shoes. My daughter and I tried wearing flip flops, and they are hard to walk in. Our feet tired out fast.
You gotta do it, the drops are incredible. Whats really funny is seeing the people who wear a poncho on the ride.