Is there a way to keep this scenario from happening (other than not allowing users to connect a switch to their jack):
host -> user switch -> main switch -> router
We actually had this happen last night. In the user switch, a user connected one end of a cable to port 4 and the other end to port 3. This effectively brought the network down at this branch.
I've got a test setup here and I've implemented storm control, but this isn't keeping it from happening. I don't think bpduguard or bpdufilter will work either considering the port that the user switch connects to is already a designated port for spanning tree and forwarding.
Any suggestions or other tricks that could keep this from happening in the future?