Litter tray misses!

Have had a spate of poos being deposited just outside litter tray. In an effort to ‘re-educate’ (Tansy, we think) we have bought The World’s Best Cat Litter to replace the wood chip litter. Also, two trays in use just in case the problem is caused by overcrowding. And, have been leaving a small amount of poo in each tray to ‘mark the spot’. All poos in tray now for the past week. Maybe, maybe?