[ubuntu] Log off sftp or ssh?

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http://ubuntuforums.org – I'm using SSH to access a computer on my LAN- call it computer B. I book marked computer B on my main computer (call it compute A). Then, I unmounted computer B from computer A. I thought that would prevent me from easily getting access to computer B again without going through the Places----->Connect to Server routine. It didn't. I simply selected the book marked computer B and I was right back with access to computer B. How do I shut down the above mentioned easy access so that even though I have computer B book marked I'll still have to use the Places------>Connect to Server proc (Hardware)