Personally I would always use slabs.
This was the reply to a similar thread recently:
" It depends on your setup, but for maximum fox proofing I'd do:
- place the run on slabs and if it isn't absolutely massive and heavy I'd want to secure it in place by screwing to a wall etc.
- only using very thick timber (50 x 50mm minimum) and very good mesh - 1/2 x 1/2 inch 19g or thicker, galvanised weld mesh
- double meshing... mesh the inside, then the outside. Triple meshing is an option too... I'd double mesh the inside (overlapping so that the gap is tiny) and single mesh the outside as it's easier for a predator to rip it off than push it off.
- every opening needs multiple padbolts... i.e the big thick bolts which allow you to put a padlock on. If it's only animals you're concerned about you could just used carabiner clips. Foxes can undo catches, and they can also pry a door open if they can get hold with their teeth so you'll want it secured bottom & top at least
- any openings from hutch to run or shed to aviary etc I would personally use runaround doors, even if you are not planning to use runaround tubes. The standard size is designed that a fox cannot get through and it also would be much harder to widen than just a standard hole in the wood.
- motion sensor lights, preferably with a noise!
- fence spikes (
http://www.amazon.co.uk/Fence-Wall-S...?tag=spikes-21)
- fox repellent... foxwatch gets good reviews (
http://foxrepellentexpert.com/store/)
Of course it's probably impractical to do it all, so the minimum I'd want is slabs, strong timber/mesh, double meshing and padbolts. "
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