Re: Backyard practice?
I do a great deal of casting practice on the grass and have for years. If the grass gets tall or weedy just prepare to lose some yarn flies and retie leaders and/or tippet a lot. I use tapered leaders but always just the very short leaders I used to just toss away.
As for fly lines, no matter what you use just know they will discolor. Ain't no getting around that. Still, despite the discoloration my lines all shoot very well. All it takes is occasional cleaning with mild soap, a once-over with an SA microabrasive cleaning pad (if the line you use has a finish that is the same material to the core and not a slick surface treatment) and good line dressing. I use Glide or Rio Agent X that is a bit more work to apply but it works and lasts a long time. My thinking is that a slick line that isn't greasy attracts less dirt and doesn't wear itself out over the guides and grass.
I have a couple of once very bright, Optic Orange XXD and Expert Distance lines that are a few years old and are far from pretty to look at yet still they act like some of the newer lines I've used. How they fish or float I can't say as I use them mainly on the grass.