Arelith

People often use current fixtures as replacement to the walls and barricades.

What about to add defensive fixtures? Wooden palisade and stone wall?

-would be very hard to bash (dmg reduction, really lots of hps)
-extremely heavy, assembly required on place
-you could "lock it" so it cannot be moved by players around

And add also balista fixture. It would harm all in direct linie from its shot, but it would do three times more dmg to the fixtures allowing to shorten time needed to get past defensive placements.

If we wanted them to be available, they would be

Seriously, there's a reason they're not - namely that if they were, they'd spring up everywhere in no time at all. Building walls appears to be a popular hobby for adventurers.