'Williams' Double Yellow' is in my mind the best hardy, blackspot resistant, double-yellow, once-blooming rose. It spreads invasively as Jack Thomas points out which is cause for concern. For me it looses the lower half of its leaves by the end of summer to a leaf spot disease (possibly alternaria leafspot) but this by no means is cause for concern as the plant is still ornamental. It produced hips for me last year which was unusual and they ripened quickly and turned black as in Rosa spinosissima which further leads me (height of plant, density of growth, hip shape and color, resistance to blackspot) to believe that this rose has growth characteristics more closely related to R.spinosissima than to R. foetida. In my limited experience, I have not seen rose hips on any form of R. foetida that I have come across.