A lot of people are going to hate me for this...
Why not make all construction signs entirely passable; construction cannot be completed if there is an item or unit within the clipping area.
The long-popular exploit of the construction-sign hunting fence will vanish. It will be far easier to navigate a small, busy claim.
It will also be possible to block a construction by standing in it's area; this makes some sense, as you can't expect to be able to build a house while a raving barbarian is charging at you. The increase in opportunities to grief will be similar to the ones that are being gotten rid of with the removal of construction fences. The net effect would be a marginal decrease in griefing, as one would have to go up and grief in person...
The large-scale effect of this would be to make hunting-goods much more valuable. A lesser effect would be less getting locked in invisible construction mazes.