add bypass (password) Teleportation Circle

[shaggy1987]

In one of the campaigns I play in I have a underground hideout and I want to protect it. It's a long cave tunnel with a said tunnel.
I was thinking of placing a (permanent) Teleportation Circle on both sides and teleport them just past the other circle.
That way they will never see the said tunnel. The problem is that the Teleportation Circle would teleport me to.
My quistion is: "Is there a way to add a bypass (for instance a password) on it, like with other traps?
In what way can I do that and what do I need to do it?

the trap layout:

|-----------------------------------------------------------------------|
. . . . . . . . . . . . . . . .a2.b1. . . .a1.b2. . . . . . . . . . . . . . . . . .
|---------------------------------\.\-----------------------------------|
,',',',',',',',',',',',',',',',',',',',',',',',','\.\',',',',',',',',',',', ',',',',',',',',',',',',',
teleport a1 to a2 and b1 to b2.