But the LORD has become my fortress, and my God the rock in whom I take refuge.

Notice: God did not build me a fortress to protect me from those who do evil.  HE has become my fortress.  In the Hebrew “has become” is in the past perfect tense, meaning “completely accomplished now”.  No matter where we are in life, or what has plagued us, we always have our fortress.  No one is taking these walls down!  GOD has completely accomplished now that He is our fortress.