The Ground (Prop) does have the collision option but does not appear to work properly.

Suggestion:
Use the Grouping Tool to duplicate the Ground, i.e., make a new prop, and then use the collision option for the new prop and the foot.  This combo appears to work properly.

cheers,
dr geep
;=]

Remember ... "With Poser, all things are possible, and poseable!"

cheers,

dr geep ... :o]

edited 10/5/2019