As far as I know, Kings Worthy records for this sort of date are not available online.
I too am struggling to find a marriage for Robert & Mary
anywhere in Hampshire

I have found the following baptism records in a register transcript that I have:
Elizabeth bapt 26 Mar 1699,
Thomas bpt 18 Feb 1702/3
John bapt 1 Mar 1704.5
Sarah bpt 14 Nov 1707
Robert bpt 26 Dec 1713
all in Kings Worthy. Robert is recorded as living in Abbots Worthy.
I did find a baptism in 1669 for a Robert Garrat - in Andover, which a few parishes away.
Robert son of Robert (!) bpt 26 Aug 1669
If Robert & Mary married in a parish other than Kings Worthy, it might be difficult to trace if the records for that parish do not survive at that date

I have checked the Winchester diocese Marriage allegations which begin in 1683, without luck.
Nell