since official records in scotland did not start until 1855 there will be no marriage certificate for robert and ann
the old parish records(OPR's) are the place to look for records before this
these can patchy at best
births and marriages are not too bad but deaths are another story , also these record are only church of scotland i believe(i.e. not catholic)
i think some of the splinter church records are noted as well
as for that 1845 marriage

one letter out ?
seems to be the right place and the right time(william born 1847)
what are the chances of a another robert wright and ann mckeith/mckeich
marriage in perthshire at that time ?
i think it would be worth a look at that OPR marriage on scotlandspeople

ev