How do I detect moles or voles in my garden?

Typical vole signs / presence
Smooth, convex shaped runs without any evidence of root debris. The run - on one or both sides - will quickly solidify (inside 5 minutes to 5 hours) with the adjacent ground.

Typical mole signs / presence
The runs are roughly oval in shape, loose and almost certainly show root debris presence. Runs will solidify slowly (inside 1 to 7 days) and then only on one side of the run. Any 30 cm runs one has previously exposed may well be 'under' burrowed. Careful finger probing will establish the new run(s).