Alternatively you can use a lamp dimmer. You would just have your UTH applied to the bottom of your tank (make sure you have an air gap between the bottom of the tank and the floor/shelf/whatever surface your tank is sitting on) and the UTH would plug directly into either a dimmer or thermostat and then the dimmer or thermostat would be plugged into the wall.
If you choose a dimmer, you will need to frequently check the temperatures (measure by either a digital thermometer with a probe or an infrared temperature gun) and tweak the level of power your UTH is receiving to provide your gecko with the correct temps. A thermostat would be less effort because it would regulate the temperature for you (although it's still very important to measure your temps with one of the devices mentioned, thermostats can and do malfunction). Dimmers are cheaper, thermostats require less effort. Pros and cons to either. I've used both in the past with good success.