entrenched

adjectives

dug in
is similar to
immune to attack; impregnable
"gunners raked the beach from invulnerable positions on the cliffs"
established firmly and securely
"the entrenched power of the nobility"
is similar to
brought about or set up or accepted; especially long established
"the established social order"; "distrust the constituted authority"; "a team established as a member of a major league"; "enjoyed his prestige as an established writer"; "an established precedent"; "the established Church"