How captured druid can be chained so that he can't shapeshift to something that slips out of bondage, 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 access to magic. Tight rooms are out of question and barbarians can't afford to use high level character(s) as guards, at least not all the time.

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