Leaning on the ground is perfectly OK to clear fouled plugs, it's how you go about it, and you don't do it at full throttle - unless you want to pay some big, big bills.
John Deakin articles on the subject.
https://www.avweb.com/features/pelic...e-your-engine/
https://www.avweb.com/flight-safety/...-all-together/
On the big radials during cruise it was normal to carry out what was called a "high power burn out" to ensure the plugs were kept clean.