2001 Ford Explorer Car rolls in park

Sounds like the shifter cable is out of adjustment or something is coming apart that controls the cable. First lift and support vehicle so you can get under it to inspect where the cable attaches to the trans. Be sure it is ok and nothing has broken. Next you will need to remove the lower shield so you can gain access to the steering column from under the dash. Inspect where the cable attaches to the column, some Explorers loosen up there and it can cause what you describe