You need to have a Ruler Base for your longarm. I don’t put anything on my rulers. I simply hold them. Don’t have slippage. Longarm rulers are not really big, they aren’t made for cutting. My longest one is 12”. I can hold it in place, stop and move my hands or the ruler as needed. The base is a necessity though. Gives you a flat ( base) to give you a firm place to hold the rulers. You’ve asked about longarm rulers but not mentioned what longarm you have? I always check with my dealer or the company website first for any tools to use with my machine. ( HQ Avante)
my dealer is always willing to let me try out the rulers or give me a little lesson to learn to use tools and I know I’m getting what will work best with my machine.