Use a u lock to lock the back tire and frame around the pole you are locking it to then lace a cable lock through the front tire onto the u lock and then lock the u lock.
How to lock a bike to a car bike rack.
The several lock systems that i mentioned you should get are not just for your bikes but for your bike racks too.
This should help protect your bike your car and your carrier.
So make sure your carrier is also secured to your vehicle.
You can have an externally accessible tow loop retrofitted to the car and then you could lock the bike with a cable through that loop.
You now have a bike to car lock.
Then push one end of the cable through the front wheel pass one loop through the other loop and secure the first loop to the main lock.
From here just thread the padded chain through the trunk loop the bike carrier and your bike and padlock the ends of the chain together.
Whenever possible be sure to leave your car and bike in a well lit and populated area.
Many bike racks include a locking mechanism but an additional lock is always a good idea.
Attach a u lock or chain around the rear wheel the frame and the bike rack as above.
Lock your bike rack to your car.
Check that what you are locking your bike to is strong and sturdy.
Not only does it make thieft more difficult but it a visual deterrent to bike thieves in the first place.
A hitch rack provides a good lever that can be effectively used to snap the rack or the hitch off to take the bikes and if the bikes are damaged in the process the thief just walks away leaving a mess.
Remove anything that is removable from your bike.
Google your vehicle make and model and add the words tow hooks or tow points for ideas or talk to a qualified auto mechanic dealer.