It's not a problem that monsters do destroy ladders in addition to other "furniture".Yeah, this did not work out as intended. We'll fix this.
It just happens so damn quickly. Iron / titanium ladders should be much tougher than wooden ladders. Right now it takes like 1 swing to demolish any ladder of any kind.
I see no harm in making the player "figure out" the solution of building a sturdier ladder when the wooden ones are destroyed too quickly. =)
Same applies to other "defensive" structures.
Building something like a door to secure against monsters hardly slows them down. Yet the whole point of a door is to keep things out... at least for a noticeable amount of time.
I suggest adding some iron / titanium based doors to the next DLC. Really really tough doors. If they do their job I won't care if they cost 100-150 iron for a 1 block door. =)