We covered a teepee type
We covered a teepee type structure and placed it in the middle of his litterbox . . . his own fire hydrant, so he could lift his leg. He adapted instantly. (Note: if you can't keep up with overturning and changing the paper daily, don't use the clumping cat litter under the paper! Clumping litter in dog paws is not a good thing.)
After a week or so, we reduced the size of the box to 4' x 2'. He has no problem using it .
When he was home alone, we left a paper-lined, cat-style, plastic litter box in the house for him. He never used it. He seemed to think it was his fancy bed. Oh well, we can't win 'em all! ~ Griffon-tastic
update: We had another Griff stay with us for a few days. She quickly learned to use the litterbox, too. It took a couple days for her to figure out that we wanted her to go INSIDE the box. Initially she was comfortable going outside but was doing her business on the indoor/outdoor carpeting leading to the box.