I just tried my first attempt at dry hopping with a rainy day IPA I brewed last week. I simply cut a grain sock down to an appropriate size, threw in 2 sanitized stainless steel washers I had, and added the 1 oz of Fuggles and .25oz of Warrior I had left over, I used pellet hops and that is why I decided to go with a sack. There is almost no hop particles floating around in the beer so the grain sack seems to be working out great. I then threw the sack into the secondary and racked right on top of it. The beer was on day 4 with S-04 (a very fast fermenting yeast) and about .002 away from my expected FG at racking time. The sack floats at the top, but the washers provide just enough weight to keep the sack submerged just under the surface. I have 12 more days in secondary and then 2-3 weeks in the bottle before I can share my result, but I'll tell you it smelled pretty good while racking!