generally nothing happen to wander, path-less, into my fort from the caverns before I've succumbed to some sort of surface invasion.
I once had a pack of naked mole dogs run right into my fort and drink all my booze. This was unexpected.
Consider the above an edit. What I meant by that was although I usually open up a flight-path from the caverns into my fortress, proper, until I actually make a walk-able path nothing is going to deliberately enter, and though stuff does happen to flap its way in, by then I'm trying to work out how to deal with the surface conditions.
Collapsing a wall into the caverns is a fun megaproject, although it does throw up huge amounts of stone. You don't need to get these out of the way if you collapse the sealing wall in such a way that it still seals the hole it fell through (you also get the mechanism and support material back this way, as they have nowhere down to go), but miscalculations can make a mess. A big hole across a cavern floor is still a good defence against anything that doesn't fly though.
I approve, for what it's worth. Although I still miss no-ramp channelling, as well. The lengths I'll go to to get an aesthetically pleasing channelled barrier set up without leaving ramp exits on my side (e.g. build a bridge over, leave t'other side with ramp exit for de-rampers, then unbuild and/or deactivate by lever the bridge, because doing the same with floors always leaves stones, and I can't abide such messy tailings being left all over the place, inaccessibly, and a minor caveat to the whole prior approval that I gave) are often a mini-project of their own. Especially if I feel I must also smooth everything I create (and possibly speed the arrival of the surface invaders, due to fortess wealth? ...never quite worked out if I've done that, but I'm sure I must be paying a price of some kind, as well as the time spent getting it all sorted).
Er. A point was in there, somewhere. As is grammar, honestly.