The intelligent access on the focus will not allow you lock the doors with the fob in the car. You might as well leave a sign on the car that reads "STEAL MY CAR PLEASE" because leaving the fob with the car is an invitation for theft. Even using a magnetic 'hide-a-key' won't work because the fob is still too close to the IA sensor. Your best bet is to take the fob with you.
13 Blue Flame F150 FX4 402A on 20's loaded
13 Frosted Glass Escape Ti 401A loaded
13 Performance Blue SE 201A
14 Dark Side Fusion SE 200A
L-CCC #18/HOIA #37