how do you keep the yarn ends from popping out after you weave them in and trim them ?
Weaving in ends
What kind of yarn are you using (is it slippery?)? How are you weaving the ends? How long is your weave? Certain yarns may necessitate the ends being stitched with a bit of thread. I don’t use slippery yarns but do use a lot of recycled yarns that have unplied threads. With that, or acrylics (when needed), I use a dab of FrayCheck.
ETA: neglected to mention I always use some form of dupe st to weave. Nearly impossible for ends to find their way out with that method.
cam
When I weave in the ends I used to go in and out of the purl bumps in ONE row, but they can flip right out so I just put the yarn on the yarn needle and weave it straight down the piece . It won’t move. It would take a lot of force to get them out.