I protect the liner under the ladder with a piece of 40 mil PVC cut to fit. This material can be found in the tile section of your big box home imporvement store and is sold as shower pan liner.

The walls of AG pools, when sufficiently high, are often acceptable by local codes as an effective barrier to small children accessing the pool when installed with an automatically closing gate on the ladder with a latching mechanism high enough to prevent use by a small child. These codes also usually specify that the pump/filter must be located such that they cannot be climbed to gain access to the pool.