A look at what is currently available on eBay
 TERRY NEW MATTRESS PROTECTOR COVER FULL SIZE WATERPROOF US $13.99 
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 TERRY NEW MATTRESS PROTECTOR COVER KING WATERPROOF SAFE US $18.99
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 TERRY MATTRESS PROTECTOR COVER TWIN XL SZ WATERPROOF US $11.99
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How to take care of a mattress?
When I moved into my apartment, my husband and I got a grand new, but cheap, bed. Since having it (June 2010) it's become really disgusting. There has been blood, cum, as well as dog piss (my friends dog pissed ON our bed). Obv we needed a new bed because the one we had was disgusting. We tried putting those plastic protectors on it, but I'm a really light sleeper, so any movement sound made by the plastic would wake me up. 
So how can I take care of a mattress besides using plastic bed covers?
First of all, nobody is going to see your mattress but you and your hubby when your changing sheets. If you're very concerned about the mattress not absorbing fluids, look into mattress pads that go between the sheet and mattress. They're not plastic, they're absorbent cloth material, sort of like when potty training kids or for the elderly with incontinence. Then get a nice mattress cover to go over it all (I like the thick quilted ones for my back) and then the fitted sheet.
Lastly, when you're friend comes over with the dog, don't let the dog in your bedroom. 
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