I hear many exploit came from /tmp (root directory)
How to protect this /tmp directory more secure (no exec)?
Thank you

Raq 550 uses /tmp for executing scripts from pkgs. This prevents adding nosuexec unless you remember to disable it every time you update.

On raq 4's, you will need to have the latest kernel and can create a file using dd and then mount it via a loopback interface. There are numerous how-tos over at forum.ev1servers.com. Not that you should put the file in /home not /dev as /dev is small on the raq.