Cannabis smoking

[Hornbyvilla]

Can anyone give me some advise as what to do when when you know your guests are smoking cannabis??...ok it may outside the building(just poping out for a quick ciggie)but the smell lingers in the hallway when they come back in & although they may not be smoking it in the rooms...the room still smells a bit as it is on their exhailed breath.

What would anyone reccommend saying to them?
i have read it is still a class b illegal drug & althouggh they are not smoking it in my property they are bringing it in to my property.
Any advise helpfull
Gill