Natural gas can easily fill a grill hood as it's lighter than air. On the other hand, propane is heavier and will fall from the gas grill.
So checking the gas grill is essential to prevent your house from burning down. Natural gas and propane have distinct odors so you can smell them if there's a substantial leak. However, this method isn't sufficient enough for detecting every potentially explosive leak.
You'll need a bowl containing very soapy water and a basting brush to check for gas leaks. Also, you need gas to ensure the fuel tank is filled up. Make sure your tank valve is on to pressurize your fuel lines coming from the tank to your control directly to your control valves. Don't smoke, light the gas grill, or have open flames anywhere close to this area. Now brush the soapy water over every connection and hose. This application should be gradual, while you're watching for the formation of bubbles. Wherever you see bubbles forming, there's a leak.
Several things can cause leaks from loose connections to broken or cracked hoses. As soon as you identify potential leaks, disconnect your fuel line and switch off the gas. You can tighten loose connections, but broken or cracked parts will need replacements.