Garden Bollard Base

I need to install 10 or so illuminated garden bollards (approx 500mm high).

These are to replace existing units that are wired via buried SWA.

Whats the best way to construct a decent base? - the original installation has concrete dabs under each light but these have, over time, disintegrated. Is this just because its been executed badly or is this a poor method? Would a small paving slab, drilled to allow SWA through, be a better idea?

Thoughts please?

I would be looking at concrete pads, about 2-3 inch deep if in an area not likley to get kncoked by people, maybe 6 inch if in a high traffic area. 

First hand experience tells me that if you give them too good a foundation and someone bumps with a car, then the fitting will be broken. If they are lightly set you can straighten them up again.