Obstacle Avoiding Autonomous Car- Help Needed with wiring/connection

I am trying to build an obstacle avoiding robot car with one IR sensor. I have the Arduino Uno and a Motor Sheild. All the tutorials I have seen advise to simply place the shield on top of the Arduino board. Is there any other way to connect the two. I feel that with the wires already in the ports of the Arduino board from the IR sensor, simply placing the motor shield on top won't work. I am trying to use it for a class project ( I am a teacher), so any help or advice would be greatly appreciated!

IR -sensor ??
try with “HC-SRO4 Ultrasonic Sensor”
like http://www.instructables.com/id/Arduino-Ultimate-Obstacle-Avoiding-Robot/

Get a schematic of the Arduino and the motor shield, find out which connections are common (often no all the pins are connected) and connect them with wires...

or find out which unused pins on the motor shield are available, you could solder connections for the IR sensor to them...