I'm going to be building a raised garden bed out of pressure-treated
landscaping timbers, and I wanted to know how long re-bar would last in
this material.

First off, this is for a flower garden only, not a veggie garden, so
anything leaching from the PT lumber will be of no health consequences.

Secondly, this will be in a relatively hidden part of the yard, so it
don't need to look incredibly purdy. For this reason, staining from
the metal vs. wood is also of no consequence.

I'm planning on predrilling holes through the timbers, then pounding
re-bar through and into the ground about two additional feet. So my
question is two-fold:

1. How long would this re-bar last before it rusted so badly from the
PT chemicals that it lost it's holding abilities?
2. Is there a better material I could use similar (and as cheaply) to
re-bar that wouldn't rust so badly?

The bed will be three timbers high, so roughly 6 - 9 inches in total
height.

TIA.