Leaking Keel

[zonefour]

I have begun to see the dreaded stalactites hanging from my keel which I believe to mean the cement is washing away.  Three questions:

Is there a stop-gap measure I can use until I absolutely need to dig it out and replace with new "heavy stuff"?
How do I know when it is absolutely time to dig it out and replace with heavy stuff?
Could I cut through the floorboards and make the repair?

Thank you for the combined wisdom of this group!

Scott
Green Bay