Companies like Vandgard do fence toppers like rollers (£50/m), Rotaspikes and RaptorSpikes, and fence alarms such as Rotagard – which is Climbgard with Geoquip Alpha acoustic alarm.
Vandgard Raptor SpikesVandgard RotaSpikes
Prikka Strips or SBD rated DefendaStrip are a cheaper, more subtle and less aggressive fence or wall topper.
PrikaStripDefendaStrip
Electric fence toppers are available such as Harper Challice, SBD terror rated APS Electrofence and SBD terror rated Gallagher FT60D monitored pulse. Electric fences are tensioned at about 40kg and typically have 50-95mm gaps spanning the height of the fence and 1.2-1.6M topping above that. Electric fences should be to BS1722 Part 17. For health and safety in peacetime you could put up signs, install extra fences either side to stop accidental activation and limit shocks to 5J. But post-SHTF, burglars will have to take you as they find you and if they decide to commit suicide on a giant electric fly killer that is up to them as suicide is not illegal. Vaylia resell Electrofence. Gallagher fences protect UK electricity substations.
Harper Challice electric fence topper
Barbed tape barriers delay intruders with no tools for about 18s, according to a 1974 Sandia test.
Limey Prepper - UK Preppers Handbook 
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