In that verse, the rhetorical question and answer ("Is there any other God; there is no other Rock") shows in THAT verse that "Rock" (capital "R") is being used synonymously with "a god." The point is there is but the One True God (see Commandment #1).
But "rock" doesn't always mean "God." If you think it does, you'll have a fun time explaining this verse:
"And some fell upon a rock [petra]; and as soon as it was sprung up, it withered away, because it lacked moisture." (Luke 8:6) So is Scripture saying that when the seed (the Word of God) fell upon God Himself ('there is no other Rock'), that God (the "water of life") could not sustain His own Word due to lack of moisture?
Or should we instead apply the "Elsie Rule" (see Post 445) and say that since "Rock" comes after "God" in Is. 44:8 that they are different things? But applying that rule, we have a conundrum since then "Rock" would be a different thing than "God."
Oh, the difficulties that are presented in trying to defend the "no one else but God is 'rock'" position.
I suppose when one can't discern between when it's being used as a metaphor and when it's being used literally that would make sense.
It appears we are between a rock and a hard place!
It appears we are between a rock and a hard place!
Then just WHY are you trying so hard with the Abraham = Rock thing?