Are you talking about frame quilting? On my Hinterberg carriage, I use small plastic spring clips from the hardware store that look like this:
https://www.amazon.com/Evelots-Plast...dp/B00IEG3H0W/ . I place the clamp on the carriage in front of one of the rear carriage wheels; this stops the carriage from moving forward. When I baste the top of the quilt, I am simply careful to keep a little pressure on the machine handle, pulling the machine towards me as I baste across.
Not all clamps work, depending on your setup. I bought several small plastic clamps at the big box hardware store and kept the receipt so I could return the ones that didn't work. I prefer ratchet clamps to spring clamps, but the ratchet clamps are bigger and didn't fit on my carriage well. You can use 2 clamps, one in front of each rear wheel, to ensure you don't inadvertently dislodge a single clamp while you are basting.
Of course, this works only for basting from one side to the other. I assume that's what you are wanting to do.