Monitoring Spanning Tree links

We have a set of Ethernet switches in a ring using STP, and I would like to monitor the interfaces so that I can detect failures of the links. The method that I am considering is to monitor the two interfaces that connect the ring on each switch (using .1.3.6.1.2.1.17.2.15.1.3) and alert if one of them goes to the disabled(1) state, as in normal operation they will either be forwarding(5) or blocking(2).

My questions are:

Is there a better way to achieve what I want to do?
If this is the best way to do it, how do I get OpManager to monitor only th eports that I am interested in and not all the other switch ports? I can't see a way of setting an SNMP monitor so that it will monitor, and therefore alert on, only some of the ports.

All advice gratefully received!

Regards

Andrew