Clip their wings!!! About two weeks ago I woke up to find one duck in her nest as usual and my drake missing. I called the RSPCA three times to let them know my duck was in the area somewhere and I went searching the streets myself (he'd been picked up by this time) and luckily, they brought him back to me. I had seen them both flying very small distances but didn't think they would fly over my 6 foot walls! Turned out he was looking for his mate but she was in her nest and he was confused and flew to find her (how romantic

) so I just looked up a youtube video of how to do it and It is so easy!
Make sure you clip ONE wing on each duck so that it throws them off balance when they try to fly. Do not clip the both as they can still fly

Honestly, you will feel better after doing it as you know they can't escape but also you are protecting them from hurting themselves if they decide to explore! Make sure you do not cut the 'blood feathers' which are closer to their body.