Take a 5 gallon bucket, find a small one that fits inside it with about 1 inch clearance, mix up some quick Crete and make a permanent one.
To use the buckets, make it even easier. Get a 5 pound brick, a 4 foot section of PVC, and a bucket. Connect the PVC to the brick and to the center of the bucket. Drill some holes to sink it and voilą. A bucket off the bottom that has no chemical or anything added. Again, put some eye hooks in the top and you can snag them and move them later if you want to. Or you can snag them by dragging a rope around the PVC toward the bottom.
I love taking my kids fishing, now if I could just manage to fish at the same time.