I prefer using Liquid Paper to erase the real mileage.
Then I use a red pen and write the number

 

How about raising the car on jack stands, put it in reverse and stuck the throtle wide open? Better if you do it pointing to a cliff and replacing the stands with wooden blocks. If this doesn't work, you might get lucky and insurance will pay for your totalled car.

I live in the US, but grew up in South America and this is a very common practice in other parts of the world (I'm refering to tampering with the odometer). So you never look at the mileage. You calculate the mileage and estimate plus or minus according to the overall shape of the car. You can always tell....