I was out on Friday on the Don, and as Hamish says, Polyleaders (well, Rio Versileaders) were enough to be touching bottom occasionally. (I say!!)
I started with a 3.9 ins a second and a 1" copper tube but I was a little too high so went back through with a 5.6 ins a second and just grazed the gravel every now and then.
Heavy flies also help...but keep your nylon short when using the fast sinking tips..about 3 feet, else the fly rides high.