It occurred to me that digging trenches has been part of warfare from ancient times all the way the modern day, but we don't see it much in table top gaming. Largely because there is no such thing as a portable hole. You can pick up a small section of wall and put it on a table but it's hard to make a section of the table that is lower than the rest. I think if you made a battle board and it was sufficiently thick you could build a trench in it, but would it be worth it? Is there an easier way to accomplish this that I'm not seeing.
Yes Warmachine/Hordes players build portable trenches. ...in segments. Flat tabletop but trench elevation is abstracted.
Multiple trench terrain ^ segments. It is just like building river terrain, same principle. The difference is the edge walls are much taller than they would be on river pieces.
I'm thinking about something for KOW and had a couple of ideas. First was some temple-style walls with a bold embossed pattern on it which would paint nicely. Not really temporary defences though. The other was the temporary defences built by people in the Sudan from thorn bushes (Zariba), but instead of the bushes some thick/spiky jungle plants. Zariba were usually built at the end of a days march to defend a camp or contain animals so would fit the theme of something done quickly as natural barbed wire.
One of the Oldhammer Dwarf Army books had a rule about entrenching an artillery piece. I think you had to assign an engineer (upgrade) to the cannon, then it could be upgraded with fortifications-trenching. To represent ^ that: I remember seeing people take CDs and build trench walls around them. Large round or Big oval bases (flipped over) would work just as well for such things.
I really like this idea! Nice simple way to do "3D" trenches. I have seen the warmachine trenches too. … also you should check out @Drimon 's EPIC TRENCH terrain piece!
Alternately what you could do if you have the money or time to make it (I don’t think it would be to expensive but idk) would be to make the ground of your table actually elevated and interlocking with slots for a trench price to be sat in. You would have to redo your table if you have one but if they are used a lot should be worth it. Essentially your table would be elevated a bit and be smaller pieces that interlock with a trench piece that can be substituted in sort of like a giant puzzle.
That's a cool idea but I don't think I have the time or inclination to go that far, but if I did, the same system could make a trench or a river. Rivers are something that continue to vex me. They are very important terrain pieces, tactically but they hard to model well. Usually when I play with my friends, we drape a couple neck ties (ideally blue ties) over the table to show where the river flows.