The Leupold Mark 4 is a great scope but the one thing I found it to be lacking the more I shoot at long range is a Zero Stop. Other top of the line scopes have them and I wanted to give my Mark 4 that capability.
So I made a Zero Stop Shim for the elevation turret (M1 Knob)
Out of my box of random pieces I grabbed a rubber hose washer and trimmed the inner and outer diameter to fit around the mechanics of the turret and inside the turret housing. It isn't a true zero stop since I can crank the turret about 4 MOA under zero, but it prevents a full rotation beyond zero, which is what I wanted. See pictures for more detail.
Its a cheap and simple solution that just works, I've since taken the paracord off my scope (I had just got it and I was wrapping everything at the time)