adding a new piece of timber to hardwood an existing frame

[kieranb]

I have a hardwood -stained- conservatory- with bifold doors and I need to add another piece of timber (with drip return) above the doors to stop water running down the facia and onto the door track below. (I think this is a design fault but the installation company are no longer around)

What should I fix the new piece with?

1. Tacks - should I use stainless?
2. Screws? or
3. Glue, what type?

or combinations of the above?

Many thanks

Kieran