How do you make a secert den?

Use Secret Power in front of a large tree, bush, or indents in cliffs.

To make a secret base, you need the TM Secret Power. Walk up to a indent in a wall or a large tree, and press A on it.

If you have a pokemon that knows Secret Power, it will ask you if you want to enter. If you click "yes" then that will ecome your secret base. You get Secret Power from the guy just outside of the Fiery Path on the Fallarbor side.

Once you see him, he will automatically talk to you and give Secret Power to you. This also allows you to buy Dolls and so on in Slateport City. You remember the guy that said you could be in his group if you got a certain TM? Secret Power was that TM.

You need to teach your pokemon secret power. Then with that pokemon in your party go to a mountain with a square shape etched into it press A and then it will say use secret power. Also the big trees can be used.

It's so long ago that I made one that I think its when you have a pokemon that knows hidden power

When you see a dent in a cave or a big tree have a pokemon use secret power towards it and it will become a secret base.

You must use Secret Power (TM)

The way to make a secret base (not named secret den) is to teach a Pokemon hidden power or secret power and look for a tree that has vines or a mountain with a dent and use hidden power or secret power and there is a base.

use Secter Power on a Tree that looks diffirent
a fat bush on the road or a strange indentation in the cliffs