Like this?

use strict;
use warnings;
use Data::Dumper;
my @students = (
    {
    name  => "Gil",
    college => "Yale",
    },
    {
    name  => "Gil",
    college => "Harvard",
    },
    {
    name  => "Gil",
    college => "Harvard",
    },
    );
my @unique = do { 
    my( %seenName, %seenCollege ); 
    grep { !$seenName{$_->{name}}++ or !$seenCollege{$_->{college}}++ 
+} @students};
print Dumper \@unique;
[download]

UPDATE: Sorry, got that wrong. It should be:

my @unique = do { 
    my %seen; grep { !$seen{$_->{name}}{$_->{college}}++ } @students};
[download]