my $re = qr< . _(?: FOO | BAR ) \z >x;
print "$_: ", (/$re/ ? 'true' : 'false'), $/
  for map quotemeta, qw/ dog_FOO my_dog_is_blue_BAR
                         my_dog_FOO_FOO my_dog_FOO_is_blue
                         _BAR 12345-(*65326523_BAR /;

__output__

dog_FOO: true
my_dog_is_blue_BAR: true
my_dog_FOO_FOO: true
my_dog_FOO_is_blue: false
_BAR: false
12345\-\(\*65326523_BAR: true
[download]

Check out perlre and YAPE::Regex::Explain for more info on the above regex.
HTH

_________
broquaint