How to get rid of my puppet's elastic feet while walking?

I am right now working on my first character; I am already past the designing and basic rigging stage. While it has been a smooth ride till now (thanks to the Okay Samurai tutorials), I am stuck on the walking phase. I am unable to understand why my puppet has ended up with elastic feet that streches in and out while walking. I have attached a short video. 

Need help as I have no plans to make big foot videos (bad joke intended)!