I'm making progress in fixing the first batch of backroutes for the Gold and Platinum rank - only a few more Platinum levels left to go before I can send another version to kaywhyn.
So far, the levels didn't turn out as backroute-prone as I feared - and for the few glaring ones I left open, the fixes were usually the easiest (just some extra steel / one-way arrows). For one particular level, a trap did the trick by blocking off a route. Since this was a Shadow level, I didn't want to use one of the standard L2 Shadow stompers here (the ones with the red exclamation marks), since the top part always looks like a walkable steel square. Normally, these traps go on top of terrain - having one just by itself, without actual steel under the red exclamation mark, would be confusing. Hence, I went with the red-eyes trap from L2 Cavelem instead, which does seem to go along with the L2 Shadow tileset quite nicely.