This is the last post in the "overexcited nosework alert" series; here are two more suggestions that might help in calming your dogs overexciteable behaviors while maintaining correct alerts.
You could try revisiting the the very early "imprinting" exercises that involve you holding a tin or container in your hand. Be prepared for the dog to knock into this hand, maybe even claw it or mouth it. No matter what your dog does though, hang on and keep the container as steady as possible until the dog quiets and does the alert you want. Do this for many sessions, then go back and try another container search (containers on the ground.) Is there any improvement?
You could try walking the dog on a leash into your search area. For some dogs, the presence of a leash will repress behavior somewhat, since (hopefully) they're used to slowing down and walking politely when the leash is on. Make sure your body language suggests a casual walking style other than a more formal one, so the dog understands it's free to focus forward and move around a bit, rather than be in a strict leash position. If all goes well, the dog will be slowed down enough to do a calmer alert, but not so slow that it doesn't see or pay attention to the boxes at all. A few rounds of this should get the dog a little slower; then try again off-leash and see if there has been a change.
In the long run, an enthusiastic dog will be easier to work with than a slower, less motivated one. So keep working at it, and let me know if you need help!