I haven't any real experience with it, but there's also the autovivification pragma. Because I'm not familiar with it, I would tend to use it in the narrowest possible scope:

c:\@Work\Perl\monks>perl -wMstrict -le
"use Data::Dump;
 ;;
 my %hash;
 dd \%hash;
 ;;
 if (do { no autovivification;  exists $hash{foo}{bar}{99}{x}{y} }) {
   print 'got it';
   }
 ;;
 dd \%hash;
"
{}

{}
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This also works with statement modifiers, e.g.:
    print 'got it' if do { no autovivification;  exists $hash{foo}{bar}{99}{x}{y} };