I Texas rig my decoys and use vinyl coated wire rope for the line. I am able to tie the line in a knot and leave it that way all offseason, and the line never shows any memory at all. Vinyl coated wire rope is the only true 100% memory free option I have found, and now that I made the rigs I use I wouldn't use anything else.
The only drawback is that it is more expensive than standard decoy line. There is a company that makes complete Texas rigs with wire rope:
Lifetime Decoys Texas Rigs. You can make your own for about half the price if you are willing to put in a little time.