Are you still talking about Present 29 there? The way I did it was have the first Lemming dig down the right pillar, he'll hit the steel and leave him there. With the next Lemming, dig through the beam pretty far right, then dig and put each Lemming in turn in each of the little square cells starting with the left one. With the final Lemming, there's an icicle dangling down to the left of the trap, dig above that and he'll survive the fall. Then he'll walk into the wall and turn around, then he can build over the gap and bash to the exit. Dig to release each Lemming from the square cell in turn, making sure not to break the wall to the next one, and then when they're all down, bash left to get them under the steel wall. You shouldn't be trying to get Lemmings over the gap before the bridge is built, which is why I'm having trouble seeing how you're losing a Lemming anywhere.
Make the first lemming from the right group block before the edge. Make the *last* lemming from the left group dig down the left edge of the one-way wall, then bash when he reaches the part with right-facing arrows. Build a landing platform for the right lemmings, then dig and bash under the blocker. Release the left lemmings by bashing left, then turn one round on the "step" just before the exit so he can bash to release the others.
Ah, nice. My solution was way more complicated. XD I bashed dug/mined (can't remember which now) and bashed with the left Lemmings. I used the last Lemming from there to build to turn around, bashed right and build over to make the platform. I contained the right Lemmings by digging a pit and letting one Lemming bash away the wooden step so that the Lemmings could survive the fall. Can I steal your solution for my walkthrough please? XD
I take my earlier comment back by the way. Mayhem 19, "Time to get up!" is the hardest, most annoying level in the game. Having to time those 2 bombers to perfection without a save state would be so unbelievably annoying. >_<