AGP Liner keeps falling off the rim

We emptied our 18 X 33 oval AGP to re-do the sand base and we were successful in re-hanging the beaded liner. Once 12-18 " of water accumulates, the liner falls off the pool edge. I read something about a vacuum behind the liner to hold it to the wall.... never heard of this- is this what we're doing wrong?
Are there any kind of clips that could be used to secure the liner?

Thanks for any help you can provide......