The only reason the charm was not secure after Dumbledore's death was because he was dead and everyone who had been told about Grimmauld Place after he died became a secret keeper. Then when Hermione apparated with the ministry worker into the zone around Grimmauld Place he was sort of told about the place. 

Maybe you could be the first mission? Like you contact one of us through a weird channel. And we go to meet you ready for a fight but you're actually there alone?