Off a diffuse target I think you will struggle with a CW, eye safe, visible laser at 70m although it is not impossible. After hitting your distant target the light will be scattered in all directions so the amount of light you will receive at you photodiode will be very small. I think an APD will be necessary. Have a look for an Arduino project based on the principles of a Bosch laser tape measure - it should give you some ideas. I don't have the links available at the moment.
Keith