How do I prevent my dock from hiding (a problem that just crept up)

I'm running Mavericks on an iMac and everything has been working fine until yesterday morning when my dock started to hide until I put the cursor to the bottom of th screen and then it would show itself. Then, after a while the problem went away and my dock stayed visible. This morning (Tuesday morning) it started hiding again. I should point out that I do not have hiding turned on. But at the same time, if I turn it on and then turn it right off, the doc will stay visible for a while and then it start to hide on me.

Any idea what's going on?

~ Rob