#Rendre pratiquement irrécupérable...
/summon item ~ ~1 ~ {Item:{id:"minecraft:totem_of_undying",Count:1b},PickupDelay:99999999}
#Ou encore, plus complexe (exécution continue):
/summon item ~ ~1 ~ {Tags:["noCollectable"],Item:{id:"minecraft:totem_of_undying",Count:1b},Age:0,PickupDelay:99999999}
/entitydata @e[tag=noCollectable] {Age:0,PickupDelay:99999999}
#Tout item avec le tag "noCollectable" sera concerné...