We brought this problem to Sherrill's attention several years ago. We sent them lots of pics to document the issue.
Not much can be done, really.
Unfortunately unless you are licensed for rodent control applying something like REPEL or another pepper based product would be illegal.
Of course you would also have to make multiple applications which would be costly.
The last cobra/rodent issue we had was resolved through predation. We set up our bucket in the canopy and sniped the critters.
Though in this case it was more then just the cobra, the critters were girdling 8 inch and larger stems as well.
Our experience has been that you don't have to cure their lead deficiency syndrome, just send some lead supplements their way and they tend to move on.
Barring scaring them away, there can be good eats in them tree rats.
Poly-pro & poly-ethyl seem to be preferred plastics amongst the rodents. another protective measure may be to armor them with some sort of wire. Dunno...worth exploring I guess.
Tree rats have been the bane of maple sugar producers forever here in the NE and nobody has come up with an effective solution.
Anyhow, just my 2 penny's worth.
