Albert Barnes Commentary Psalms 89:40

"Thou hast broken down all his hedges; Thou hast brought his strongholds to ruin." — Psalms 89:40 (ASV)

You have broken down all his hedges - His walls or defenses; all that he relied on for safety.

You have brought his strongholds to ruin - His towers, fortifications; defenses. The enemy has been allowed to destroy them. They are now heaps of ruins.