Defendable (adjective)
Capable of being defended.
Defensible (adjective)
capable of being defended against armed attack
Defensible (adjective)
capable of being justified
Wiktionary
Defensible (adjective)
justifiable by argument
“a morally defensible penal system”
Defensible (adjective)
able to be protected
“a fort with a defensible yard at its feet”
Oxford Dictionary