Sticky sand

Over the years I've forked out a fortune on plants. I made some mistakes along the way such as expecting plants with a need for high lighting or CO2 to thrive in conditions not suited. I've seen plants wilt and die, some just melt away. I'm sure most on forum will have suffered similar things.
I now have good lighting, CO2 where needed, water parameters suited to the tank inhabitants including the plants but I'm still suffering.
It's not that the plants are dying off as such. It's more that they all tend to come loose from the substate play sand and float to the top. OK, I do have a few Clown Corys snuffling about so some disturbance can be expected.
So, how in hell's name can I anchor the plants? I'm talking mainly things such as
Alternanthera Reinekii, Monte Carlo, Rotala Rotundifolia etc. Most of my plants are short stemmed so that it can encourage mating behaviour. The tank setup was made specifically to grow them easily. To that end I placed a fair amount of aquasoil in fine mesh bags over the area that I really wanted to get some good bushy growth, then I covered the whole lot with around 20mm of playsand. The plant free part was for the benefit of the corys.
It really gets my goat that the sand is mostly gone from over the mesh bags too. The slight rear banking front to back where the bags are placed has almost, if not actually, levelled itself out with the mesh showing.
However, each day more of the plants have floated to the top. Is there a way to sort of "pin" the plants into position so that they are secure?

Sticky sand​

Have you been looking at old PlayFish magazines again?
Dirty boy, dirty, dirty boy.

Two things. First, mixing substrates (meaning, sand over something else) is not advisable because the normal water movement will shift the sane. This occurs in all tanks, regardless of water current from a filter. The natural ecosystem allows water to move through the substrate. This is why sand will not normally compact, assuming things are correct to begin with.

Second, to the stem plant issue. Plant a sufficient length of the stem, at least 4-5 inches/10-12cm, in the sand; push them down to the glass. You don't need 4-5 inches of substrate, just push the stem down so this much is covered. As a further protection, you can use small pebble of smooth river rock. These can improve the aquascaping at the same time. Corydoras feed by sifting the sand through their mouths and gills, and they will easily sift down through a couple inches. They cannot sift the rocks/pebbles if they are big enough, and this worked in my cory tank.

BTW, what exactly are "clown cories"?

Ah, I used my own name for them. Panda Cory, but these provide hours of amusement so I nicknamed them to clowns.
Anyway, I may turn this tank into a reef tank shortly. Just doing some research first.
However much I do to make up beautiful aquascaped set-ups they are all so dreary in comparison to a marine tank.