I have a 60cms-18 gallons tank with various plants including Ammnia sp.Bonsai no hair grass instead I have Marsilea Minuta. My substrate is JBL Mando beneath it is JBL Proflora. I had the same problem in the beginning. JBL Manado is an airy substrate it will take time but in the end u'll be able to plant hairgrass. My shrimps love to dig too (never planned to have shrimps in this tank due to CO2, high lights n ferts) yet I kept on replanting till they stopped.
I started feeding (spreading) pieces of shrimp food an hour after lights out in the tank in diff.corners this keeps them occupied and they do not think abt.disturbing my plants.
Till date I find a few plants floating but I got used to this. Instead I sit back relax and enjoy my cup of coffee, watch my fish after feeding them. I replant,trim,etc. during water changes once a week.