Commit 975EA35 makes the clear physics mode arrow appear for the selected lemming no matter what its current action is, instead of only when it's a blocker.
This is of course not a full solution to the issue, but a full solution will have to come later. Ideally, I think the long term solution should be to introduce some changes to the sprites. This doesn't have to be radical changes, but perhaps the blocker looks in the direction he's facing and nods his head up and down (rather than side to side), while the digger could perhaps always perform his strokes towards a particular side (I actually feel stroking front to back would be better here, but I'm not 100% sure on this). Off the top of my head, disarmer is the only other one where the direction is ambiguous and the lemming is going to remain in play after the action; since this is an original skill, there's much less need to worry about staying close to an existing animation, perhaps disarmer needs an entirely new one.