Depends how you define secure in today's society. Are you looking for a manned gated car park : a city centre car park, on street parking or pay a few kids to look after your car for you?

The Etiad will have its own car park if you want near the ground or if you are prepared to walk 15 minutes or so there are numerous car parks behind Picadilly Station ranging from £3 and up on a Sunday.

just use one of the warehouses in the vicinity, we've parked in something similiar to gone in 60seconds for the last two years, scary as fook, but its been reyt.

You can park at the ground on a first come first served basis. It was about half full last year. Check the Man City website

DONT park at the Asda across from the stadium. There are few unofficial car parks around and some City fans park up behind the cemetery on a match day (on the road for free)

Another option would be to use the trams in Manchester if the OP doesn't mind parking further out and catching the tram to the Etihad Campus. There is a Park and Ride scheme at Ladywell tram station. Parking for 250 cars and a day return would cost you £4. Easy to get to from Warrington as well.

I'm lucky...I got a stadium parking pass.