# I suppose I must be in the $_ appreciation society :)
for ($guarantee) {
 s/this/that/g;
 s/foo/bar/g;
 #..etc.
}

# or (probably not preferable in this case, but it IS sometimes
# handy to localize $_, e.g. in File::Find 'wanted()' subroutines)

{
 local $_ = $guarantee;
 # ... some operations on $_
 $_ = $guarantee;
}