Leather spots have been used for centuries to protect furniture. One of the many references from the 18th century is an entry in the account book of Thomas Chippendale on 4 July 1768 which notes, "4 brown leather spots with gilt edges" at a cost of four shillings. Protect your fine furniture the old-fashioned way.
Leather coasters are absorbent and extremely durable. If they get really soaked, (maybe someone wasn't using a coaster and knocked a drink over, flooding your beautiful coffee table) flip them upside down and let them air dry.