Pool

My In-Laws were very sweet and bought the girls a pool this summer. Thanks Mooie and Poppie! Who knew that one little pool would be such a pain in the neck! We've had it for about a month now and the girls have only been able to get in it 2 times so far. Our backyard is less then level and filled with rocks, sand and clay. Poor Beau spent 2 Saturdays digging, raking and filling in with dirt, just to try and make it level enough to hold water (there were a few failed attempts!) We finally got it up, filled it with water just to have it magically poor over the side (still not quite sure how that happened). We lost a pump hose, which also resulted in loosing water. We finally got it full again, bought all the chemicals and waited the 24 hrs and finally enjoyed our first dip in the pool (see pictures below). The ground still wasn't level, but it seemed to at least be fine enough to hold the water and let us swim. Well after a day of rain we woke up to find the cover of the pool trying to hold in the water, so when Beau went to take the cover off, out spilled the water again!!! So know we have a half full pool just sitting in our backyard! We really don't want to have to take it down completely, the girls love it and Beau and I enjoyed it a lot too, but we have to figure out someway (inexpensively) to get it level and keep it from washing away on us! Any suggestions?