Stop and take a count at EVERY intersection and stop sign. I know mirrors aren't sexy, but I have them, I am usually lead with my family and I have gotten good at counting the number of sleds behind me. I usually check every 1/4 mile or so. If the count is low I stop and wait. Twice the wifey has gotten stuck or off the trail and both times we doubled back within 1-2 minutes to bail her out....things happen fast......
...a few years ago, we had stopped in Rockland on our way to Lake of the Coulds, it was mid-morning and a group came in looking for gas, but the restaurant was closed so they went on. We had gassed up before leaving Toivola, decided we had plenty of fuel so we headed out after a few minutes. 20 or so miles out of town, we find 1/2 of the group stopped, one with hood up, you guessed it - out of gas. Said they would wait for the rest of the group to come back. We kept riding, didn't see anyone for awhile, 20+ miles down the trail is the other half of the group. We pull up and they're surprised that "we" are not who "they" were expecting. They ask us if we saw another group? Yes! I say....20 miles back....out of gas! They were speechless. Duh!
I used to ride with a guy who never looked back...when my son was 12 we went riding with him and he would blow away from every stop sign and never look back....after a few starts/stops he had left us behind. We found our way back to the staging area (I didn't know the area...he was the "Guide") and just started loading the sleds. He pulls up with a look like "what's up why are you leaving". I just told him we were done riding for the day, didn't like being left behind in an unfamiliar area...that was the last time we rode with him. I don't think he ever understood why. Some people just don't get it!