Before I started making my own, I purchased these by Priva:  
Amazon.com: Priva Ultra Plus Waterproof Sheet...  
They are awesome.  I can tell you they have various sizes and I was able to find the smaller version at my local Rite Aid Store.     They work fine I can testify I have washed, bleached, oxycleaned, dried at high heat, and gotten rid of yucky poop and all sorts of stuff.   The work.   I have since made them using the same backing Priva does and I ripped theirs apart to see what it was and it is quilted cotton fabric with a great waterproof backing that I buy by the yard from a place in Canada.          I cannot make them for what you can buy these for.       So think about your local drug store and start looking for  the incontenient aisle.  They are used all the time.    Pick one up and try it.  

 
The one I referred to is 36 x 52 and I have 5 that I use everywhere.  I also have the 36 x 32 version or some such size.  They don't come in colors, which is why I started making them.  Some folks like to have something to match their homes, etc.    Well, since I use the same backing, anything I use on top works just fine.      It doesn't need to be made specifically for dogs.      I have washed and dried mine in excess of 100 times each.   They don't fall apart or lose their ability to work.   I don't know about others, but these work well.