How captured druid can be chained so that he can't shapeshift to something that slips throught bondages, like small snake for example? I would prefer minimum or no magic used.

Druid in question is lvl 7 and captured by nomadic barbarians with only limited acces to magic. Tight rooms are out of question and barbarians can't affort to spent high level character(s) as guard, at least not all the time.

Subquestion: if ropes (that are not metal) are used to bound druid, do they melt to new form when he shapeshifts?