Detaching RBTA

My RBTA has split twice now and I am hoping to sell two of them, but do not want to damage them removing them from the rock. Any suggestions?
Aim a powerhead at it, so it begins to 'walk'
Or if you can remove the rock, and you can see its foot, you can carefully use your finger nail
I read somewhere that you can use a credit card to try and get under the foot. It needs to be plastic as you don't want to risk damaging the foot. As soon as you get a corner started, use your finder to slowly slide under and separate the foot from the rock.