with fusible fleece, I fuse it to the backing. Then I pin the top to the sandwich, but I don't use as many pins as I normally would, since it's only the top that is likely to pleat or pucker in that case and you can watch it and smooth it out as you go along. I generally also FMQ-stitch in the ditch right before I FMQ a block then remove the pins, or if I anticipate doing some FMQ that will extend beyond individual blocks, I may stitch in the ditch over the entire quilt using a walking foot before FMQing--in which case all the pins get removed before FMQ work.
Rob