Exactly!
I cannot put glass, razor wire etc, on top of the wall as it doesn't matter if they are wrong to get up there, trespasing etc. if they cut their hand trying to get up there then you can be helf responsible - great system eh?!!
Building the wall up impacts neighbours etc. so that has to be approved etc.
By the way even warning signs do not offer protection - insurance companies usually settle out of court and up your premium rather than incur the legal costs.
Good to hear the options however.
Shug