I use closed cell packing foam. Its only free, because it seems like invariably something I buy gets shipped with this stuff. To use I tear off a small piece from a sheet. Then I tear a small hole in the middle. Next push a loop of your leader through the hole. Then twist some of the packing foam through where the loop of leader went through. I'll try to post some pictures of this later.
The one problem is that if not done right the line will twist as it is cast. Since the stuff is free this not a huge issue as you can keep changing it until you get it right.
I really feel this stuff both stays where you put it and is more easily moveable than any of the ones you buy. I also like that it does not look unnatural on the water (just like a piece of foam). If you have problems seeing it on the water, just color it with a sharpie permanent marker.