I agree with Val – a trap would probably be the best way forward. I have borrowed one before from a wildlife rescue that they used for badgers/foxes, i’m not sure how large sibes are but if they’re not much larger than a good size male border collie then they would probably fit in similar traps. Is there a wildlife rescue near by ?
nb – if you set a trap it will need someone to check it every couple of hours just incase you either a) have the dog or b) inadvertantly catch some wildlife !!
If its a farming area, I do know of someone who borrowed a fox trap from a sheep farmer once but I am not sure if this would have fitted a sibe as they were catching a bedlington terrier size dog !!