Stopchalk

full stick of Stopchalk has 10 uses and does not
replenish. When drawn across a horizontal
surface the linedrawn becomes a completely
impassable and invisible physical barrier
as wide as the line drawn and as tall as the ceiling.
If one gently places their hand on the barrier
it will feel diamond hard even though there is
no visual effect.
Lasts for as long as nothing impacts it physically
in a significant way.