My fabric liner and decorative curtain are on the same rod. The liner hangs inside the tub, while the decorative curtain hangs outside the tub. Maybe you could use a second (tension)rod for the liner and just push it to one side.....BUT..... I keep my curtains drawn across the tub until the liner dries; if you push it to one side, it will get moldy, sure as you're born....

You can also order liners than are extra long. I have a couple that are 96" long.

I use the fabric ones as well, and I buy extra-long ones from BB & Beyond. You might call for availability, if you have one in your orbit.
I make all my shower curtains, and hang them higher, and make them longer, than 72". Somehow the stock 72" square looks ungraceful to me, and I never like anything in the store anyway...
And I hang the liner on the same hooks inside the fabric curtain.

Duh! I should have googled 84" liner....I see now they are mass produced. This is for a guest bath that gets little use so I will let it dry before it is stacked back. The thread about using burlap has inspired me for a shower curtain. I am seeing a cream trimmed out with a wide grosgrain ribbon. Must. Learn. my. sewing. machine. again.

Smiles:)

No "duh" required!
Here are some considerations...

If you are doing two panels, you could split the liner down the middle and hang it half and half. Otherwise, you will have to use two rods.
Unless you want the liner to stay closed while the drapery sits open, in which case you would need two rods. And then you might want to make a pretty sheer panel to run along the liner's rod in front of the liner and stay closed, which will look more finished and furnished, with your two side panels open.

If you do split the liner, put velcro dots along the split edge so the halves will overlap enough to discourage water coming through them...and (here's another "duh!") make sure the one on the same side as the shower head overlaps the other, so the water goes past the break instead of into it.