locking 3d models location in real world

Hi,

So, basically i wanna track a big object like a car and watch through mobile phone or hololens, to see what's inside the car.

I'm doing this by sticking an image target at the car's door. that way I can place the 3d model on the real car.

There is two problems. The 3d model is bit shaky (moving a bit now and then) and when i go to other side of the car, the 3d model disappears, because the camera cannot track the tracking image anymore.

So I was thinking could it be somehow possible to "lock" the 3d model, when it's first tracked on right place? so when you go behind the car, the app is not tracking anymore, it just shows the model in it's right place.

I don't know how to do that, but I was thinking maybe someone here could have an idea how to do it?

Or maybe someone has a better idea how to reach the wanted results?