严密

The programme is well packed.

Security was tight.

closely guarded

wall blocking

tight defence

A strict blockade of the passage of information has been imposed.

His ideas are a bit lax.

closely follow the development of the situation

put under close surveillance; keep close watch (over); keep a sharp lookout

keep a close guard on (sb)

impose a tight blockade; impose a watertight embargo

take strict precautions (against)

closely-knit argument

carefully-laid plan

tighten up rules and regulations