use Hash::Util qw[ lock_keys ];;

$My::Space::fred = 12345;;
%My::Space::hash = 1 .. 10;;
@My::Space::array = 1 .. 10;;

lock_keys( %My::Space:: );;

print $My::Space::fred;;
12345

print $My::Space::fred = 23456;;
23456

print $My::Space::fred;;
23456

print $My::Space::freddy = 1234;;
Attempt to access disallowed key 'freddy' in a restricted hash at (eval 18) line 1, <STDIN> line 10.