Uma combinação de DENYs e um GRANT. Por exemplo:
DENY SELECT ON schema::[dbo] TO [user_name]
DENY SELECT ON schema::[other_schema] TO [user_name]
GRANT SELECT ON schema::[safe_schema] TO [user_name]
DENY SELECT ON schema::[dbo] TO [user_name]
DENY SELECT ON schema::[other_schema] TO [user_name]
GRANT SELECT ON schema::[safe_schema] TO [user_name]