Protect SRX from Stealth scans

Hi,

I have searched for a clear cut answer to this question but cannot seem to find one.

I want to be able to protect our SRX Firewalls from stealth scans via nmap or a similar program that will silently look for listening ports or even open ports. Is there a very quick, easy method for this or some easy to read document somewhere that will state the best way to complete this please?

Thanks