highlighting duplicates if the cells match between multiple columns

I have two columns in a table and want to highlight if there are any duplicates between both...
Column A is 'locations' and Column B is 'dates' i want to make sure there are not two people in the same location, on the same date..

For example, in the two columns (letters for locations, numbers for dates) below i would want to highlight Z 1
Z 1
D 1
H 3
W 6
B 3
Z 1
J 1
L 4
Z 2

any help is much appreciated!!!! conditional formatting would be preferable!!

i was thinking of doing a concatenation column of the two but trying to avoid if i could... people play about with the spreadsheets and will probably end up un-hiding the column and 'tinkering'

this worked.

i also found a method where you can enter the formula straight into the CF...

'=COUNTIFS($D:$D,$D1,$E:$E,$E1)>1