Funny thing?
According to the list, no eidolon forms possess the 'body' item slot:
http://www.d20pfsrd.com/magic-items#table-magic-item-slots-for-animals
So... this item is useless?
http://www.d20pfsrd.com/magic-items/wondrous-items/wondrous-items/h-l/harne ss-eidolon-anchoring
