I have a Mathews Vertix, and just got the bow restrung with ABB Premium Strings. When I got my bow back, I double checked the D Loop location on my string with my T square and it was off from the shop, I was able to slide it back to where it should be somewhat easily. My question is, do I need to take it back to the shop and have them tighten the loop in its place now? Or will it tighten around the string over time shooting it? I have about 100 shots through it since moving the loop and haven't had any issues yet, just don't want to get into my stand and all of a sudden it moved without me knowing it. Thanks!
Take a pair of needle nose pliers and tighten it yourself. Make the d loop location with a mark of silver paint marker so you have a point of reference.
It should tighten up as you draw the bow if it's tied properly, a 100 shots now should have it pretty tight. If it does move on you again, until you can take it back to the shop and have them tie it on properly, you can adjust the height by twisting it around the string. Rather than just trying to slide it. One direction will make it climb the string and the other will lower it. I would mark it like trial153 suggests. Silver sharpie, or you could even take some serving or dental floss and tie just outside of both knots. Just something to mark where it should be. In the future, ask for them to tie in at least a bottom "soft nock". Having a soft nock on the bottom, or one on both top and bottom, also makes it easy to know if the d-loop has moved. Soft nock also helps to prevent nock pinch at full draw, they are put on inside the d-loop gap.
I had a related problem last year with a new bow. D-loop installed by the bow shop was sliding up or or pinching my nock. I am not sure if it was the serving or dloop. either way, I tied in a small knot above and below my nock and inside the d-loop knots. Prevented arrow pinch and I believe stopped all problems as everything is staying put.