The best solution in my opinion is using those GPS running stopwatch, they are smart enough to give very accurate run distances and speed as well as terrain inclination and such.
Some of them are equipped with heart monitor and can record efficiently your health performance i e your heart fitness etc.
They are expensive but they are worth, just make sure to buy those with Genuine GPS censor.
Any cellphone or tablet could do the same job if equipped with GP censor.
I have never owed any GPS stopwatch i was just fascinated by them 4 years ago, but my fascination ended when I stopped jogging so I forgot them.
Amazon.com: GPS Running Watches