my 04 disco doesn't seem to have retaining screws for the rear disc where the screws should be looks like a stud no bolt head or allen wrench hole should I just try and whack it loose

 

Good, hopefully someone removed that useless PIA. You can get the rotor free by hitting the back with a rubber mallet, or a steel mallet if you're replacing the discs.

 

the PO probably snapped the screw try to get it out. they are only there to keep the rotor from falling on someone's foot on the assembly line.

 

haha so true... there are a lot of useless parts on vehicles that helped with the assembly of the vehicle. On my S60R it's a thing called the "exhaust bracket of death" which basically goes across the exhaust under the car, if you snag it which many do, it sends the resonator into the $700 prop shaft.

 

here a great one Ford, they put a plug in the tranny fill whole as the tranny are shipping (looks like a fishing bobber).
Well when it get installed in the car they just jam the fill tube in pushing the stopper into the tranny pan, does bother anything it just lays there.
The first filter change "Surprise were the hell does this go?".
I used to screw with guys for hours (all the ITT grads) would try even hole in the valve body to see where it would fit, before I would tell them it was trash.

 

haha!