So using mine markers you can stack sandbags into the air . This is easily recreated using the shovel and sandbags and of course placing mine markers on top of sandbags

To replicate
step by step
Step 1. Build a sandbag fortifaction of any sort
Step 2. place the mine marker on the sandbags
Step 3. build the a second sandbag fortification
Step 4. rinse and repeat

by doing this you can climb into the air endlessly into the air via ent stacking
Collision being on the mine markers allows this to be done