How to attach unexposed deck frame to post

Hi, I'm planning to build a decking area behind the garage in my back garden, and would like some advice on how best to attach the frame to the posts where I cannot access the "front" of the frame to screw through into the post. The area I am decking is enclosed on 3 sides by the garage to the left, my shared fence with the neighbour to the back and another fence to the right as you look at it. So essentially, I won't be able to get round the "back" of the decking on those 3 sides. The videos I have watched suggest securing the frame to the posts with 100mm coach screws by screwing through the frame and into the posts. So how best can I attach the frame to the posts if I'm unable to get round to the front of the frame to do this? Thanks Sam