Linux: Prevent a background process from being stopped after closing SSH client

I'm working on a linux machine through SSH (Putty). I need to leave a process running during the night, so I thought I could do that by starting the process in background (with an ampersand at the end of the command) and redirecting stdout to a file. To my surprise, that doesn't work. As soon as I close the Putty window, the process is stopped.

Linux: How to measure actual memory usage of an application or process?

How do you measure the memory usage of an application or process in Linux? I've read here that "ps" is not an accurate tool to use for this intent.

Closing another process listener

Is there any possibility to create a listener for closing another process?