Unhitching safely on deep grass - slight slope

Wow thanks for all the input. I purchased another set of the large rubber chock blocks from harbor freight for additional holding power. I'll also pay closer attention to how I put them down and unhitch the truck. Lastly, I'm going to use a large 2x14 board on the bottom under my lynx blocks under the trailer jack, that should distribute the load a little better. I'm headed to the Gorge now, I'll let you all know how it went!
Scott