Our two little buggers used to dig out the plants all the time but we
discovered if you just put a layer of rocks (not huge ones or pebbles but
inbetween sized ones) on top of the soil they won't bother with the plant
anymore.  This technique saved Fred our rubber tree plant -
 
Good luck
Dawnie the prego-puff
Fern & Gaston "but grandma doesn't do this so we dig up her plants instead!"
[Posted in FML issue 1912]