Please stop clan hopping

My clan gets like a billion join/leave per day.
We like being an open clan, but there are those who just abuse it and join/leave within minutes.
Some say it's connected to "friends in need" achievement but that doesn't really matter.

Can you please make it that joining clan is timer based like anything else.
Make it so that you can join only once 15 minutes (or even longer).

While at it, feel free to add the Report button to clan talk also.
We've started getting join/spamm/leave idiots.