I'm going to posit an -a declension here, coining a noun "p'at-a", "stone"
[pre]
SG PL
NOM p'at-a p'at-u
GEN p'at-ak' p'at-uk'
DAT p'at-abi p'at-ob
INST p'at-awa p'at-uma
[/pre]
Sošn-a wek'ne-s p'at-awa
Soshna:NOM fish-HAB stone-INST
"Soshna fishes with a stone"
Sošn-a gaas wek'ne-d p'at-ak'
Soshna:NOM NEG.DO fish-3sOBJ stone-GEN
"Soshna doesn't have a stone"