A small amount of research into the institution of marriage will teach you that among the most feared beings in the universe is a man's mother-in-law. The simple fact is that no man is ever good enough for this creature's daughter, and she wants to make sure you know this at every opportunity.
of the best ways for a mother-in-law to trap the husband is at his own home - this is commonly called a "visit." On these visits, the mother-in-law will do her best to occupy both the hideaway sofa bed and the husband's free time, berating him with such seemily innocuous questions as, "Are you wearing THAT?" "Have you considered a different job?" and "Where are your pants?" Each question, of course, is designed to generate enough discomfort in the husband that he will abandon his wife, so that she may find a more suitable mate, such as Fabio, Stevie Wonder, or Charlemagne's corpse.
But with this new product, the Allergen Garden, the husband can finally create an environment that the mother-in-law will find untenable. This is biological warfare at its marital best.
In the Allergen Garden, normally stored outdoors, a husband can grow such items as ragweed, timothy grass, and common mildew and mold (on a grout base). Cats and dogs, unfortunately, do not grow well when planted. The Allergen Garden, therefore, would have a canister of dander from each of those common pets, with an easy-open lid. Low-maintenance (and higher-cost) versions would simply have cannisters of the pollen/spores of the afore-mentioned offenders.
When the mother-in-law plans a visit, this garden can be brought inside the home and placed on a shelf behind a specially-designed vent in the HVAC system, spreading the pollen from your garden, and the pet dander, all over the house.
Of course, to protect the married couple, the Allergen Garden would also come with a supply of basic anti-inflammatories, such as Sudafed and Benadryl.
With her immune system thrown into hyperdrive by her allergies, the mother-in-law's visit will surely be cut short. And, with any luck, Pavlovian training will teach her to at least stay in a hotel for her future visits, allowing the husband some "me time." And time at home will be gloriously spent watching the mother-in-law sniffle and snork herself half to death.
Eventually, if plans go well, she should stay away entirely.