These liners are build to endure extreme water pressure, different weather,etc. However their strength depends on the pool size and brand. In my personal experience, intex pools are more sturdy than bestway pools but are a bit more expensive.
The intex pool liners consist of three layers, the outer and inner layers are extra thick PVC layers, supported by a middle High Strength Polyester Mesh. This adds a lot of strength to these liners than the traditional ones, which are not designed to endure such water pressures since they are used in inground ponds or in completely framed, wooden ponds.. However it should be noted that this type of liner comes in only pools that are greater than a 100 gallons.
Here's a pic to help you understand.
As for my fish, the pacu and snakehead do occasionally hit the pool liber at high speeds but don't have the strength to tear it. However this behaviour has decreased a lot eversince they have grown and become accustomed to quick human movements in the surroundings of the pool, doors opening quickly or closing with bang,etc. Otherwise when they were little this behaviour was more common.
Moreover the sound and vibration caused by my waterfall also helps in reducing the affects of incoming vibrations and large sounds caused by our recklessness, the main reason why my fish become skittish.
EDIT: just to give you a example of how strong these pool liners are, my previous 1700 gallon intex pool pond had three screws horizontally stuck beneath it, but even the extreme high pressure of water acting downwards couldn't tear it for 4 months straight.
if these kiddy pools can resist the wild behaviour of little brats then they can most definitely house some much well mannered monster fish
