Quilting with a Ruler

I've been quilting the shop sample for my beginning quilting class. Much of it is quilted in the ditch - easy peasy. But I wanted to stitch some diagonal lines through the blocks, too. On the nine patch blocks, this is not so hard - I just aim for the fabric intersections. BUT, how do I quilt the diagonal line onto the border without marking?

I decided to use an acrylic ruler, lining it up to the left so that the presser foot rests against it. I used my left hand to both hold the ruler and the fabric in place as I guided the quilt under the needle. I used my right hand as usual, guiding the quilt along.
Here's another shot showing how this worked. I know longarm quilters often use rulers to guide them. So I figured I give it a shot on my midarm machine. The only problem I had was slippage of the ruler. If I wasn't careful, the ruler would slide on the fabric and get out of whack. So I was VERY careful and it worked! Maybe next time I'll put some grippers of some sort on the back of the ruler to help prevent slippage.

I finished the quilting this morning, made the binding, and stitched it on. The plan is to deliver it to the shop tomorrow.