Do you know of any districts or schools that require a minimum personal PR for it's distance coaches? Although most coaches will be long past their competitive days what would you look for in terms of how fast they've run in their live? My guess is you'd want a male coach who has broken 17 and maybe 20 for female coaches.
Or do you base it solely on their results? I can't imagine a XC coach who has never ran sub 18 coaching guys to sub 18.