Problems with ORCAD Layout

[S.T.]

Hi there,
on my design I use Obstacles (Copper Pour, Copper Area and Free Tracks) for
some connections (connectiosn with high amps...).
All these obstacles nets are assigned.
I planned to place the high power areas an some important connectiosn and
let the autorouter of ORCAD Layout do the rest.
For the pre-routed tracks I can lock them and the autorouter do not affect
them.
But the obstacles (it semms as if only the copper pours and copper areas are
affected) are removed by the autorouter.
Can I lock them or how can I prevent the autorouter to delete the obstacles
?

Thanks in advance
S.T.