That's why instead they use a "marking knife". Basically a knife with a very sharp point that is only sharpened on one side. (That way the back is flat to ride against the ruler, square, or whatnot.)
The problem is that these knives generally cost between $10 and $50, and a good toolbox would be stocked with 2-3 of them. (Left, right, and ambidextrous)That certainly adds up! (Here's an example from a popular catalog for comparison.)
The solution I came up with is not only made 100% free using stuff you'd normally throw in the trash, but the blades are replaceable, the handle is nice and big for people with arthritis, AND the whole thing can safely go with you in your pocket!
So what's the big secret, then? Re-engineer your spent utility knife blades!!!
Step 1: SAFETY WARNING
This project involves potentially rusty razor sharp objects, modifying tools beyond their intended purpose, hazardous chemicals, flying sparks, and possibly feeding a Mogwai after midnight. If you do not feel qualified or safe doing any of the above, please surf away from this page (and probably this entire site) and take up a more relaxed hobby like perhaps macrome or counting the number of leaves on your front porch.
If, however, you're willing to take responsibility for your own foolishness in copycatting frightening stuff you find on the internet, then you have come to the right place. Welcome aboard, my friend!