Before going into a more detailed discussion, I'd like to make one thing clear: it's pretty obviously the case that mushers are tampering with their trackers, whether it's covering them up so they can't transmit, pulling batteries, turning them off, whatever - I don't know specifically what they're doing but the extremely high "failure" rate during this race is not matched by any other races going on at the moment. It may be the case that they're using different hardware for the Quest than they are for the other races, but it seems unlikely that they're using different Spot Messengers for the Quest than they've used for any other race this season, or that it's just the result of random chance that there are more outages in the front of the pack than in the back.
To be clear, not every outage is the result of monkey business - there have been some honest tracker failures during the race. But this post is about the ones that were the result of tampering.
The trackers are required equipment during the race. A team cannot check into a checkpoint without theirs, just as they can't check in without a sleeping bag, snow shoes, axe, etc. The rules don't say that the tracker can't be turned off, as far as I know. But let's say that there's going to be a new rule that the trackers must not be interfered with. How would you determine whether or not there was a real failure, or if someone hid their tracker in a cooker for most of their trip? How can you tell whether or not a tracker was covered deliberately? You can tell if batteries really are dead but you can't tell if someone's chosen to swap in some dead batteries (at least not without marking and identifying "official" batteries, a logistical headache) to make it look like the battery died on the trail. The possibility of developing a mount that would hold the tracker in a place that couldn't be covered by accident has been raised but the first time I mentioned it to someone who's done that trail his immediate answer was "It would snap off very soon."
Instituting rules you can't enforce is a pretty terrible idea, and I don't think the Quest should penalize teams for tampering with trackers unless they can provide very strong evidence that there actually was tampering. On the other hand I do think that over the longer term this is not good for the race. I believe that GPS tracking is largely responsible for transforming distance mushing into a spectator sport, and that that's resulted in increased donations and merchandise revenues, not to mention less tangible things like community-building. I hope that someone can figure out a way to deal with this.