i really liked this question...this person has got the message all good gardeners have especially in the 21 st century which is to work alongside nature , where possible , not against it. i really hate that " what poisons are available so i can grow perfect Hostas ? " attitude.

specific to Echinella i don t know but would off the top of me head suggest trying the following slug/snail ignoring herbacious perennials...

Helleborus , Chrysanthemum maximum , Solidago , Achillea , (hardy) Geranium,
Stachys ,Purple Loostrife (forgot the latin) , Ferns , Aster novae angliae (new england daisy) , Campanula ....

there must be hundreds and hundreds more.