I like the door idea...
]]>All pits is expensive to cross ($1800/tile), but presents a big problem. The robber can see all the way across the giant pit, can rule out vault locations, and will probably opt to go around the pits. You can't do dogs + pits, so you'd end up with dogs + concrete. But that's about the same price to pass as all concrete.
With pits/concrete, you're splitting the difference and forcing an average buy of $1500/tile.
You could also try something the robber isn't expecting like steel walls or powered doors. I've done checkerboard doors/power and that's pretty good because crowbars are rare and robbers don't tend to bring that many. Slightly cheaper at $1250/tile.
]]>Players dont tend to acquire them (ladders) through failed attempts on their homes so would be robbers are forced to pay full price ($1800) for them.
Everything else (except explosives to a certain extent) are available in mass quantities as suicide robbers drop them regularly.
Edit: atrocious grammer
edit dit: GRAMMAR
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