they have the small animal play grounds in Tesco at the moment at £6.50 I think. Mine can jump over it but now i only use it opened out to stop them getting behind the telly and chewing wires. As long as you don't leave them unattended it should be ok.
I use it in the garden a lot, but once, when cleaning out their cage i went inside to bring out a sponge and got back to only one piggie pow-pow I eventually checked their cage and saw her happily munching on grass. it seems she got bored of waiting for me to put her back and jumped over it and got back into her cage! :... phew!