Mostly im worried of colleagues that might steal my work to present it as their own in their portfolio! And 72lpi isnt really doing anything in that case
Oh I see.
Okay, so a few things come to mind:
1) Stop worrying. Worry is a type of fear, and it's a Biblical principle that what you fear will come upon you (Job 3:25).
2) As a practical step, you can put a watermark in your online images as a previous poster suggested. And you can do that in such a way that it can't be easily edited out of the image.
3) If you want to go another step, you can use a service that will allow you to password-protect your image collections (I don't recall of Flickr does that or not). You could then supply the portfolio link along with the password only to the people you want to give access to. Then after you know they don't need access to it anymore, you can change the password.