My older machine had this problem, so I put a thick piece of tape on either side of the bar so it could not move, then removed the sticky off the bar, with a little alcohol when I was done.

I have more success when I mark my cross hatching. I have tried the walking foot with the guide & maybe I need more practise but it didn't quite fit the bill for me. I love cross hatching on a quilt.

For a small cross hatch, I use the edge of the presser foot and adjust the needle position until I get the size I want. For a larger I use the blue painter's tape -- I use either 1" (which is really not quite an inch) or 1 1/2" size (there is a narrower size but I prefer the edge of the presser foot to the small one). I sometimes slip a pin in the tape if the tape comes unstuck.

The thinnest I have found is 1". Is thinner available?

I have used this tape and followed the design. It doesn't stick great so I use a washable glue stick to hold it in place. I use it for crib and small size quilts.
http://frogtape.com/news/article/fro...-diy-magazines

cross hatch quilting
 

I use disappearing ink when I'm doing it right away but have also used blue painter's tape.

There is three quarters painter's tape.