My personal recommendation with dubias is not letting them free roam the cage unless you're setting them free in front of him and he's getting them right away. They are excellent at hiding, much more so than crickets. Might be a good idea to get a feeding cup or two that you can use to keep the dubia in the enclosure without the worry of them burrowing into a plant's dirt. This nice person from the UK makes these awesome feeder cups: https://www.facebook.com/chameleonbugbar/
Thank you for the recommendation! Noted on dubias being able to hide and burrow into plants.