As in the title, show me pics of your parking sensors! I have a box of aftermarket sensors, I've installed similar kit before on my mate's VW Passat, but there it was a lot easier as there was plastic trim on the bumper and we just needed to match up with location of factory holes in the bumper underneath that trim.
I'd rather not take whole bumper off just to install those sensors, as it means spending more time on the Jag, which I don't really have Is there anything behind the bumper that I have to be aware of while positioning the sensors?

 

Access is very easy, no need to remove the bumper. Lie on the ground, stick your head under the bumper and you'll see there are very few obstacles once you're away from the exhausts and steel bumper mounting brackets. I decided to install only 2 sensors, centered about 800mm apart and they do a great job. To get them nearer to the corners means they are too close to the exhausts in my opinion, but otherwise it wouldn't be too hard to position 4. I used the 20mm hole bit provided in the after-market kit, measured at least 4 times, and positioned masking tape to avoid the drill slipping. I admit it took me 2 cups of coffee and a bit of self-psyching before finally drilling the holes in my otherwise unmarked bumper!

I've painted them with touch-up and I think they look OK (see images attached).

Cheers,
Tony.