@crs_7 I think what they're saying is your dog can't produce merle puppies at all because if they have the merle gene at all it is expressed. The only puppy in the litter that got the merle gene was the merle puppy.
@mitchell You could try searching for a folding dog pool.
The pool is good until the puppies start walking and can climb out (between 2-4weeks) after that you'll need a larger space. You want to use an absorbent but breathable material under the puppies that they ideally can't crawl under and...