I would compare a Town staying with the same lawyer for a 3-5 year period, much like people stay with the same general physician for years for "continuity of care."
Annual bidding out of the Town Attorney position is ludicrous. By the time one Attorney has familiarized themselves with that Town's unique Ordinances (several hundred pages usually); they would be shopping around immediately?
It is the same reason most local governments in North Carolina bid their auditing contract on a three year cycle; the upfront cost (time and personal) to prepare for providing services is mitigated by the second and third years of having general framework in place. Swapping auditing firms every year would see an immediate bump of 20-30% in cost without a correlated 20-30% increase in value of service.
More information about formatting options