How about a combination of the two?

if ( ref($var) && $var->isa("Some::Package") )
{
    $var->someMethod();
}
[download]

Or better yet:

my $sub;
if ( ref($var) && ($sub = $var->can("someMethod")) )
{
    $sub->();
}
else
{
    die "Method someMethod not found."
}
[download]

Of course you don't have to capture the return of "can" but it can be convenient.