In game, these sorts of things overlap with several other skills, primarily Tech Use, so making it as a skill could make a lot of things a lot less useful or redundant.
Might explain why siege regiments have tech-use as a standard skill… although (a) I'd make that explicit, and (b) a lot of what you're talking about is demolitions rather than earth-moving.
Then you need to deal with players who spend a lot of points into it and suddenly have an urged to erect an Abatis or tank ditch every hundred meters or dig a trench and bunker network every time combat lasts past a few rounds just for the lulz.
Oh, yes. This is for 'you've got a couple of hours to prepare, how well do you do?' tests, not Deathwatch Imperial Fist Techmarine Combat Feng Shui that somehow magically makes antique furniture immune to bolter fire.
If you really need to implement some sort of rules for it, a skill is the wrong way to go about doing it. It should be based more on a combinations of the soldiers Srt/Tou bonuses, the terrain and whatever tool he has on hand. Make an equation for that to figure out how long it takes them to make X number of foxholes or move X amount of dirt.
Fair point. The main driver for a decent trench (i.e. more than shell scrape) is going to be 'hours of labour', which, I'd imagine, works kind of like the rules for double-time marching (just on the grounds that it's the only rules in the book for how long a player can keep at a strenuous activity).
The only reason I said Trade skill was that trade skill is used for crafting…
Poor Quality Entrenchment: Shell Scrape (Cover vs 1 direction, prone only)
Common Quality Entrenchment: Foxhole (Cover vs front and sides, not necessarily prone)
Good Quality Entrenchment: Trench (Cover vs front, sides, rear, better than normal armour)
Grenade sump: Per test for cover to count against grenades thrown into the trench?
Camo: Bonus to concealment checks?