I Found It!

I just stumbled across the verses that intrigued me some time back.

Compare Psalm 71:3 and Psalm 31:3 (written with middle part scrunched). Switch tsaddi and dalet and consider that hand-written vav's and yud's are very similar.

הֱיֵה לִי לְצוּר מָעוֹן    לָבוֹאתָּמִידצִוִּיתָ  לְהוֹשִׁיעֵנִי
הֱיֵה לִי לְצוּר-מָעוֹז     לְבֵיתמְצוּדוֹת   לְהוֹשִׁיעֵנִי

Or simply leave out vav's and yud's and an alef and you get,

לבתמדצת
or
לבתמצדת

first is "be for me a rock of strength, and for a house of defense(s) to save me"

second is "be for me a strong habitation, to come continually, you commanded to save me"

Also I find interesting that in the Psalms you can often change the line breaks and verse breaks without changing the meaning.