StreamOfTheSky
Adventurer
Ah, another one - if you're high enough level for it, Shades can duplicate Instant Summons, without the pesky material component. Shades itself has no material or focus components, so you can (in theory) Arcane Mark a Bag of Holding, Portable Hole, or some other storage device, cast Shades in lockup to make a shadow sapphire, crush it, and summon your stuff with an 80% success rate (96%, if you are prepared to try twice, 99.2% if you're prepared to try three times - 100% or better, with certain PrC's and feats).
Yikes, if you're that high level, you might also find Sequester useful. Sequester :: d20srd.org
Or you could use a Gem Jump spell, leaving the gem somewhere safe, get captured. Look around the place to become familiar enough with it, call out the command word to teleport back to the gem, and then use teleport or greater teleport and bring all your friends back with you.
I was assuming this was for lower levels. If not, there's lots of stuff you can do to make physical walls useless.