Hi, im just about to do the same thing, as i have just got some live plants,
I have read to put some river rocks,pebbles , that are not too small so they can swallow them on the soil, so that the chameleon can not get to the dirt. hope that helps.
I got some river rocks form Morrisons - they come in net bags. They are sometimes buy on get one free too. I always soak mine first in hot soapy water and rinse well before pressing them down onto the soil.
I get nylon window screen, I cut big circles ( or other shape, depending on the pot shape ), then I cut a slit to the center, and a small hole in the center. I put this over the soil and cut off the excess so there is a fringe to tuck into the pot. Then I pile big round smooth "river rock" on the surface to keep it in place.
The rocks get taken out and washed about once a week; the screen too as needed. This also keeps gravid girls from secretly laying a clutch in a Schefflera.
Excuse my ignorance but why do you cover the soil? Be patient with me I just received my Veil for Christmas - we presently have an umbrella plant in his cage.
I took the plant out of the container, thoroughtly rinsed off the roots, and repotted it in soil with no fertilizer, extra ingredients etc. I made a point of asking the gardening centre for just plain soil with no additives. The water I mist on the leaves makes a perfect little drinking post for Schultzi and seems to be working well.
Hope I'm doing ok as the "covering soil on plants" really caught my attention.
I am still in the process of setting up my enclosure. I was advised to cover the soil on my plants as Chameleons can ingest the soil which can cause serious problems. I have now covered my plants with a layer of pebbles and then a Layer of Mesh on top!