vba - Excel format rule highlight duplicates based on each date column entry -

this excel doc kind of guestbook, there numerous people's names , date visited on (written 11/17/2014).

the doc sorted date, there 100 or 200 names 11/17/2014, 200 or 11/18/2014... goes on bunch of consecutive dates.

i want write formatting rule highlights if there name duplicates during duration of each day in date column. rid of duplicates, , have accurate representation of people visiting per day.

things tried:
regular dupe checker in conditional formatting - easy run dupe check within 1 column. dupe check based on 2 columns. there many dupes visitors returning daily.

the built-in formatting rule custom formula writer - easy "highlight occurrences column cell , column b cell equal" not if 2 cell patterns occurred more once.

the macro writer - i'm pretty rusty on visualbasic might faster @ generic dupe checking 100k or entries manually highlighting each day range.

tl;dr - highlight 'name' , 'date' pattern occur more once.

any suggestions?

conditional formatting formula be:

=if(countifs($a:$a,$a1,$b:$b,$b1)>1, true,false) 

dates in column "a", names in column "b", no difference if other way around, add conditional formatting whilst having range selected , active in cell "a1". slow though....