Currently, ramming a wall is about getting lucky enough for the target not to notice your ram before it's dry. Sure, you could in theory defend it, but let's face it, 24 hours is a bit too long for guard duty.
So, I propose to remove the luck from the equation. Make rams invulnerable while drying, so they can't be destroyed if they're spotted. Instead, you'd have to wait for them to dry before you can remove them. Obviously, you should be able to tell when that'll be, like if you right click a wet ram it'll say "this ram will be dry in X hours and Y minutes". The general idea is to make rams a method for scheduling battles, either you log in when it's dry and face the attackers who will come at the same time if they intend to use the ram, or you stay logged out and let them ram the wall uncontested.
Possible issues and solutions:
- invulnerable rams could be used for making impenetrable vaults - give rams a messy hitbox so they can't form a hermetic seal
- the opponent might wall your ram - build multiple rams, they're cheaper than walls; alternatively, wall your ram and drop an idol inside the wall so you can port in (to be replaced with something better when the current fast travel is replaced)
- the opponent might jump your wall - remove god damned wall jumping already, seriously
- criminals can still switch vaults to evade summoning, since it takes 24h to break one - rebuilding one's hearth should extend duration of scents by 24 hours