All the scopes mentioned here so far have some form of zero stop. NightForce has a very sophisticated clutch mechanism that is fantastic. Huskemaw has a ring on the turret tower that screws up against the bottom of the turret cap (like the lock ring on a reloading die). Both of them can be set precisely to your base zero range, or a few clicks low whichever you prefer (my zero for hunting is 200 yards, but I want to be able to dial down to 100 if I decide I want to thread a needle). The Vortex system is not quite as fancy, but still satisfies the need: the stem of the elevation turret has a groove machined into it, into which you insert as many shims (they come with the scope) as it takes to fill the space after you have zeroed the rig. All this is concealed under the turret cap, and the end result is that you will only be able to go a partial turn below your zero setting. If you get lost in your dialing, just turn down until it stops then come up to your zero. It works just fine on all 4 of mine.
