I zeroed the one I had similar to yours using a McKenzie buck archery target. If I remember correctly, those Golf range finders work at the standard flag stick height at the hole. Not sure how one could vary that. Laser range finders aren't all that expensive anymore. Even the cheap ones work well out to 400-500 yards which is probably further than you need one. The one I got is a Bushnell I picked up on sale for right at $200. I saw several for from just over $60 to some in the $500 range. I grabbed up the Bushnell because it had great reviews for being durable in all weather conditions. Luck has me hunting in some pretty crappy weather most times, that being bad luck, so my equipment needs to be able to stand up to that.

Now, you have a little refiguring to do on how you want to set ranges. You don't mess with the string again. You set the string to your length and that's where it stays. You get the ranges by the height of the target within the aperture. The ranges will be comparable to the target height. The one you have pictured is actually backwards as far as the range hash marks. The shorter the target appears in the aperture, the further it is. So if you have it set at 50 yards minimum for a 4 foot target such as a Mule deer, at 50 yards the mule deer back will be flush with the top of the aperture. And so on.