How check if URL is running ok before try open it?

Hello, I decided to make a pre-URL caller into my script, so when user try link to another URL, instead show these annoying http errors (when URL off), I could direct him to more user friendly environment. I checked FOPEN($url-name,'R') command, but in some cases it will pop up fire-walls alerts for users who uses firewalls, when FOPEN is executed. I would like to try more silent tricks for this task, and appreciate any help. Mig