One question about 'Stealth servers'

[许腾]

Dear all,
As a beginner of BIND, I'm writing to ask one question about 'Stealth servers'. To avoid the access failures arising from the broken down of Authoritative Name servers, I'd like to run Stealth servers as back up. My question is how could I set the Stealth servers as non-priority so that these Stealth servers could not be accessed unless the Authoritative Name servers are broken down? The 'forward' configuration item could set the servers as priority, is there another configuration item could do the contrary thing? Looking forward to your reply!

Best wishes,
Teng