The Smalley marriages are online, but there's no sign of Samuel and Mary's marriage (pity, because it's one of those registers where the vicar's added a lot of interesting comments):
http://www.archive.org/stream/derbys...e/n11/mode/2up
The IGI has the following submitted record:
SAMUEL RODGER
Male
Marriages:
Spouse: MARY CLARK
Marriage: 13 AUG 1781 Staveley, Derby, England
There's a transcription of the Staveley marriages online, but the groom's surname is shown as Redgate:
http://homepages.rootsweb.ancestry.c...eley/rmarr.htm
and FamilySearch Record Search also has it as Redgate:
http://search.labs.familysearch.org/...archType=exact
You'd need to see the actual registers to check what the surname actually looks like.
Staveley isn't all that close to Smalley (about 25 miles away), so it may not be the right marriage.