Prevent entering from an adjacent room, if the way is blocked, if tar or orbs are present? That would block access in those level 24 rooms though (though having looked at them, it appears access is blocked already
) Tar can of course grow, but never appears to be at the edge, in an accessable location, on the first turn.
If Beethro were allowed to clear the square he's on, and the tar square, this presents the potential that he starts a room with a tar baby right next to him, and nowhere to move. Bad room design though...
Or, Beethro could slip off the orb/tar automatically (hey, they're slippy) upon entering. Could be used for automatically placing Beethro in a non edge square if he is forced to tar surf first.