How do I prevent chalk pastel from getting smudged? I made a piece of work with chalk pastels recently. Sadly, I left it unattended on an occasion and my cats ended up approaching my sketchbook. Some of my work was smudged. On another occasion when I brought it to school for my exam, two students came to see it on two random occasions, tried to see if it's "real" by smudging it with their finger. By the time I tried to tell them not to, they had already done it.

Is there anything I can do to protect the chalk pastel from getting smudged? 

Do take in mind that I am not looking forward to ideas about covering the work with another sheet of paper, primarily because of the situation I spoke of above. Rather than preventing hazards from getting to my work, I want to know if I can stop my work from smudging.
Once you've finished your work, if you need to protect it from being smudged, use Fixative Spray that is made for specifically this purpose. Hairspray will also work in a pinch.

Only do this once you're finished though - since it will make it near impossible to add more chalk once it's done. If you need to transport unfinished work, do so in a tight folder, with another blank piece of paper placed carefully over the top of your work (with a bit of masking tape around the edges for extra security).