Hi fishingfromakay,
It really depends on what you are trying to protect, and from whom, and how serious you are about protecting your personal information.
Certainly, following NoBoMac's suggestion is a good one, but if you are logging into a work VPN then simply having a "work" account won't necessarily protect your "personal" account from the administrators at work.
A more secure method would be to run a Virtual Machine on your iMac for your work-related work, thereby limiting your work's access to the VM. But even this is not perfectly secure.
When I have a folder that I want to be truly secure, and portable, I make a compressed and encrypted tar of it and then split it into subfiles that can be more easily transmitted to another location. Personally, I wrote scripts that employ tar, bzip2, gpg2, shasum, split, cat, and diff to perform these tasks automatically, securely, and robustly, and then additional scripts that merge, decrypt, uncompress, and unpack the tar archive at the other end. As the encrypted, compressed, tar archive is encrypted using 4096 bit RSA secret keys, it is secure from prying eyes if that is what you are worried about. So, you make the encrypted archive, delete the original folder, and then use your iMac for work confident that no prying eyes will be able to recover your personal folder's material. When you are done with using your iMac for work, you can then decrypt and unpack the archive recovering your original personal folder.
...just other options...
Solouki