Which preposition to use with outguards

from Occurrences 1%

The distance of the outguard from the support likewise is governed by the terrain, but in general may be said to be from 300 to 400 yards.

on Occurrences 1%

26 Holland, to gain your friendship, is content To be our outguard on the Continent; She from her fellow-provinces would go, Rather than hazard to have you her foe.

Which preposition to use with  outguards