Cloth drop sheets:

Cheaply available through dry-cleaning businesses, where they are sold by the pound. Ask for 'damaged sheets'. Drycleaners typically 'rent' sheets to camps, lodges, hotels, and when their useful life has wore thin, are sold off. And yes, they are freshly laundered. When you buy them (typically $ 1.50/lb.) pat yourself on your recycling-conscious back for having due regard for the environment.

This pillow-sized bundle is ten pounds worth and ample for a small room - more than enough for wallpapering. And even enough leftover to make up the spare room when inlaws surprise you.

Use dropsheets to protect flooring and carpeting - they pick up and absorb:

• adhesive
• water
• spilled beer
• more absorbent than painters' canvas dropcloths (which are siliconized and water-resistant)
• don't count on these thin sheets for holding back paint spills

Over time, these dropsheets will wax ratty, so tear them up and use as pocket-sized rags. Keep one in your back pocket. Be sure to remove before you go downtown with your in-laws. Should you forget to do so, your inlaws will also wax ratty.

...which may not be a bad thing. Especially if they said that they were only staying for the weekend, and here it is already next Thursday.

If you find that the old 'rag-in-back-pocket' trick doesn't embarrass them into waning or otherwise leaving, use your intrinsic charm to convince them of the satisfaction that can be derived from doing a great wallpapering job. Assuming that they (correctly) interpret this as a subtle hint to lend you a hand, they'll be packing soon enough.

Should it be that your charm is mostly wasted on them - in that they ignore your hint or pretend not to hear you over the pay-per-view movie on the TV (the one-you-paid-for-that-they-are-viewing) - go immediately to contingency plan B. Take down the family portraits and memorabilia after they retire for the evening. Come the morrow, pay note to and relish with glee their reaction upon arising and facing the horrid spectacle that awaits them with a silent solemnity the morning next..

Also consider the 'sheet de resistance' that you have in " Contingency Plan C:

How to French-sheet a Bed When All Other Methods Fail."