How critical is it to apply flea spot on to the back of the neck? My Border Collie has a long thick coat and holding it back in a parting is bad enough but he also refuses to keep still. Even with two of us he wriggles so much that its difficult to get it all on skin rather than hair. He happily rolls over for his tummy tickling and it would much easier to apply it say under his front leg where there isnt much hair. Is there any reason why this would not work? Thanks!