Seeking advice on cat shield install

I ordered a cat shield and would like to have someone I stall it ASAP. What tips do you have for making sure there is no rattle/vibration after? Some people say to just use washers, but I've read in multiple posts that washers alone don't address the issue. Seems like I e also read that you have to adjust the muffler some so that it doesn't rattle?

What is the best type of place to have this installed (muffler shop, body shop, etc?) and what should be done specifically to prevent the dreaded rattling?

Unfortunately I just don't have the time to mess with this myself or I'd try my hand at the install. But I just spent a lot of money to get a new engine installed and I've been increasingly paranoid about the catalytic converter theft.

Thanks for your input.