We add '-able' to mark an ability and some prefix 'un-/non-/in-/..' to mark the negotiation. But I can't find in any dictionary I know and can reach the definition/translation of an adjactive(?) meaning a 'thing, that can't be lost/missed'. 'Lost' in meaning 'made unable to found (fast)'.
I tried variants 'unlosable', 'unmissable' and some semi-fantastic words, but couldn't find a definition/translation suitable for the purpose. The word is looked for to be a title/name/definition, so I can't split it more than 1 word. What word can you recommend me to use?