Of course, leasing makes sense for present day objects being unearthed. They are clearly the property of the landowners, possibly the government, where they are buried. It could regulate the trade and if provenance and context made things more valuable, then care and caution might even pay off.

For properties rightfully taken, according to the laws of the time, ages ago, this would simply be another money grab - and is, as always, complicated by the issues of who lived where when. Should macedonians have the right to Alexander's artifacts found in India? Or should the Indians? Finders-Keepers is a naive, but at least consistent, way to play a game. The Elgin Marbles and whatever else was put in museums in the 1800s and 1900s should all stay there unless the Greeks want to rent it back. Similarly, we shouldn't allow to arbitrary time-frame claims by ethnicities over territory - and we should aim to prevent wars and settle current land need issues by the relatively civilized means of rents and leases.