Nobody is going to pull the ladder up and setting it down the other side. You are going to rope down the other side.
To scale a 30 foot wall you need a 35 foot extension ladder for the 12 foot setback needed for stability. The ladder would weigh about 80 LBS. Putting one of those on a fence will cause a lot of noise as you pull the extension up and bang it on the fence. It will be enough to trigger the sensors. Climbing it will also trigger sensors. Roping down the other side will need mountain climbing experience and lots of luck. That 30 foot fall will kill.
No doubt there’s various walls and steel or whatever fencing utilized depending on the area’s. One thing for sure you won’t see a caravan of hundreds trying to get over it.