Dry Hopping questions

When dry hopping if I use 1oz pellets vs 1 oz whole hops, is it the same? Or are pellets more concentrated and therefore you would need more than 1oz of whole hops to equal 1ox of hop pellets?
And I read that putting a marble or something similar in the hop bag to keep it weighed down and make easier to retreieve it from the carboy is a good idea - only problem is I dont have any marbles. Any suggestions on what I can use as a substitute? Would rocks or river rocks present too many issues, even if sanitized?
Thanks in advance.

1oz is 1oz regardless of hop type. However whole hops will soak up more of you beer. Simply your preference. I love whole hops my buddy likes the pellets. Pellets are easier to work with usually though it seems.
As far as marbles for weight, you can also use a piece or pieces of something stainless. Nuts, bolts, washers. Just make sure they are horribly clean and sanitized.

Wrong... 1 oz. pellets lend a little more bitterness than 1 oz. leaf hops. I think both versions are fine for all additions, but I tend to prefer pellets at flameout and in the dryhop.

For weighing down the bag, stainless steel soup spoons would work. But if you're using a carboy instead of a bucket, it could be difficult to add/remove from the tiny neck.