AuraSeer said:
Holding a shapeshifter or spellcaster by nonmagical means is difficult in any situation, and nearly impossible at high levels. A druid could turn into a strong form to damage its enclosure, and then into a small form to slip out. A caster with a Silent Teleport (or Silent Word of Recall) could get out even if he were bound, gagged, blindfolded, tied in a sack, and hung upside down from a tree.
If you really want to make somebody stay put, turn him to stone.
Or dominate him. Feeblemind should work as well. Then there is the "hostage" solution: If one escapes we will punish all - works well on LG PCs. (Our paladin was set on defying a slaver. She relented when he started to punish the bard for her actions.)