In reply to MarvinJ:
Take a look on the Lattice Training YouTube channel and look for an episode with Yves Gravelle about 6 months ago on "arm lifting". Uses a pinch block or crimp block attached to a weight pin on the ground, so very rental friendly.
I've seen a good increase in my pinch and crimp strength over the past 6 months, and it's felt like there's very little chance of injury since I'm dealing with tailored below body weight loads.
