Peening copper rod

[glynn]

This is probably obvious to those of you who do it regularly, but...

I have to fix two sheets of bronze to a block of teak for my anchor fitting, and the plans call for 3/8ths copper rod peened over at both ends.
My questions are:

How much longer do I leave the rod before attacking it with a hammer, and
How do I keep everything tight while I beat the second end?

Thanks again in advance,

Glynn