Where are they coming loose? Pinching is not just a simple thing...it really does take practice and the correct tool to do it well enough. You can't just squash them with pliers and hope they hold firm. They won't. Get a good crimper, grab some wire similar to what you are working with, and practice on some 2" to 3" pieces. You will get it. Spend $5 for connectors.
Don't be insulted by pbj. He's been at it for too long.