How about training with the judgmental training simulators that offer the capability of employing shoot-back cannons? Having rounds coming in your direction and actually striking the shield adds a whole new dimension to the term "reality based training." This is the type of exercise that truly allows one to identify both the strengths, and maybe some operator weaknesses, that are inherent in shield work.
The life expectancy of these Level III portable shields mirrors the personal body armor that you presently wear. The conventional wisdom states five years, and naturally that is affected by care and maintenance. If you leave it in the rain or sun, the ballistic properties will diminish in time and not give you the longevity it should. Treat it as you would your personal body armor, and it will last five years or longer.
The Spartans utilized the shield to its fullest potential. It served not only as protective equipment, but also as a tool of intimidation. We can use it in much the same manner. A well-equipped, well-trained officer is perceived by the bad guys as an unstoppable foe and a professional warrior. That perception works in our favor, engenders respect, and more often than not causes our adversary to capitulate rather than escalate. This piece of equipment is a must for each officer on the street. I do not advocate carrying the shield on every call, but to have the ability to instantly deploy it, especially on felony calls, just makes good police sense. If cost is a factor (how much is an officer's life worth?) and precludes you from having a shield in every vehicle, it should at least be in a sector or supervisor's vehicle for quick deployment. Follow the example of King Leonidas and his fellow Spartans and include a shield in your tool kit. No warrior should be without one!