Well some times it Bobs under as little bites happen, but as soon as it takes off under, then set the hook..
1 m is what I used to use in George's river for mullet.
I guess take a look at the guys next to you, and use that depth?
Have a small weight at the end of the line and a hook about 20 cm above I suppose.
You could use two hooks so you are getting two depths