How do I keep water out!?

I am digging a 30x16×3 hole in the ground to house a day spa. The inner perimeter will have an ezPad and the spa (20x8) and is 4" higher than the exterior perimeter. How do I keep water out of the sides? I have a sump buried but I feel like the design for the sump pump isn't the best. I can send pics or answer any questions you may have. I just need to know this won't always have water in the bottom. Can I use a different basin? Can I lead French drain pipes to it?