Razor wire

Razor Wire is the answer when you get serious about security,It is relatively cheap, but viciously effective.
Razor wire series

Razor Wire around the perimeter is enough to deter any would be vandal, robber or saboteur. Razor Wire is made from a corrosion resistant galvanized steel cutting ribbon wrapped around a core of galvanized spring steel wire.
It's impossible to cut without highly specialized tools, and even then it's a slow, dangerous job. Razor Wire is a long lasting and very effective barrier technology, known and trusted by security professionals.