Chain and enough rope. The river is'nt all that fast right up there so with the tight rocking chair anchor you should be fine. Not sure why you could'nt hold bottom, unless you were under the power lines by chinook landing, it's deep and fast there, otherwise most of the river is ok.
Another area tto watch is phoca rock, and up at the fishery area and up at bonneville. These areas require a good size rocking chair anchor with 4-6 feet of chain, a good sized bouy and 250-300' of rope. you may only have 200' out, but always have the needed length. The slighter the angle to the bottom the better the changes of holding. Above 205 is a quickie wrapped with sardine, prawn spinners, reg. spinners, alvins Mostly in fall) tolled herring, plug cut. Not to assume anything, but It's closed above 205 for chinook right now.
Take caution anchoring in deep fast water. Keep a knife handy to cut the rope if
an embergency happens.
Good luck!
GBS