Wizarding gardens have to be routinely “de-gnomed” or the gnarly little potato-head creatures will take over. Fantastic beast expert Newt Scamander wrote that gnomes should be caught and swung around in the air, then tossed over a fence or wall (FB).
Harry, Ron, Fred and George de-gnomed the garden at the Burrow as a punishment for flying Mr Weasley's car to rescue Harry. Ron explained to Harry that making the gnomes dizzy keeps them from finding their way back to their old holes in the ground. But Harry noticed the gnomes returned almost immediately: "In the field far below he could see a gang of gnomes sneaking one by one back through the Weasleys' hedge" (CS3).
They seemed to treat the de-gnoming as a competition of who could throw their gnome farthest. When Harry was bitten by a gnome and couldn't shake the creature off his finger, he managed to toss it 50 feet (CS3).
Molly Weasley consulted Gilderoy Lockhart's book Gilderoy Lockhart's Guide to Household Pests when it was time to de-gnome the garden, but she never got a chance to tell the boys what his method was (CS3).