Here is an innovative idea to measure distance. Instead of using ultrasound or laser, instructable user Jones Electronic used RF signals. What he did is this: He made an RF transceiver pair. The first transceiver sends a signal with 434 MHz amplitude modulated frequency. When the second transceiver receives this signal, it answers with another signal at 868 MHz frequency. The first transceiver then receives this signal and can calculate the distance by the delay. The writer says that he can achieve a precision of about 5 meters in 1 km range, which is frankly awesome. More in this link.