I have a 2" tall acrylic liner in the bottom of my current stand that has saved me more than once, but I used a shower curtain to line the bottom of my old 90G and it worked like a charm. Same concept, but even cheaper than pond liner if your stand is not too large.
Keep in mind that many shower curtains do have anti-microbial treatments, so don't go trying to use any of the water that may have come in contact.