I am having trouble keeping the Mark stable underneath my body. Any tips?

Does the Mark feel like it is wobbling underneath your body?

If you are having difficulty keeping the Mark stable as you lay over the tool, that will impact the effectiveness of the release because there likely will not be enough pressure applied to your psoas and iliacus muscles. Here are some tips to improve this:

1. Check the surface you are on. A squishier surface (like a carpet) allows the Mark to wobble a bit and also absorbs some of the force and pressure that would otherwise be applied to your muscles. If you can be on a firmer surface (like a hardwood floor with a yoga mat), that will help improve the stability of the tool and help you "feel it" more.
2. If lying on a carpet is your only option, use your hand to apply upward pressure from underneath the handle to keep the platform of the Mark flat on the ground so the tip presses vertically into your body. This should also make the tool more stable so you can deliver the proper amount of pressure later when you press down on the handle to rotate the tip. Note that the platform will come off the ground when using the handle, but having it be flat and stable on the ground first is necessary before rotating the tip.
3. Use your hand to hold the Mark near the base of the handle as you are getting positioned over the tool on the ground. If it wobbles a little, lift your hips up off of the floor and (again) use your hand to help reposition the tool with the platform flat on the ground. Continue to hold it with your hand as you lower your body back down over the Mark. Ensure that the platform is flat before removing your hand from holding the tool in place.
4. Consider changing where you are distributing your body weight when lying over the Mark. If you shift your weight too much toward the handle, that is going to encourage the Mark to rotate before it is securely in position underneath you. Shifting your body weight a little bit in the opposite direction can help find the proper balance when lying over the Mark so it can be stable and deliver the pressure needed to your muscles.

Using the Mark is a new skill that you are learning. Keeping the tool stable will get easier very quickly as you keep practicing and using the tips we shared above.