From my experience, you're always chasing these. The minute you block one like you said, they change. Some processors will allow you to use wildcards in place of some characters, so if you have some that are close and they just change the last few digits, then you might be able to put wildcard characters in the last few spots. Other than that, you might be able to create (or have your processor create) some more specific rules if they're always from a particular area, or you can put in rules to escalate authorizations for those dollar amounts, etc.
Good luck as this is really frustrating.
"The reason I talk to myself is because I'm the only one whose answers I accept."
- George Carlin