On a TV program, they described a case in the USA where a man went missing, presumed murdered; four years later the police was told that he might be buried in his garden, the home had meanwhile be sold to new owners, so the police asked them politely for permission to dig up their garden, and the new owners agree.
What would happen if the owners disagreed? Would the police get a search warrant (when it is quite clear that the new owners of the house are under no suspicion whatsoever)?
Now if the new owners disagreed because there are things in their garden, like marijuana plants, that they don't want the police to see, would there be any way to let police in without getting into trouble for these plants?