You want to go into first person mode to stop your forward momentum on the jump so you don't fall off the fence. Once you get on the first part of the fence face the first barb wire part you need to jump to and save so you can reload if you fall off. There's a certain area where you have to land and sometimes you can even jump all the way and get stuck where there is no collision. Once you get to that part of the fence face the next part of the fence and save again in case you fall. This part is the most difficult and inconsistent part of the fence as there is a small barrier where there is no collision where you have to land. Go into 3rd person mode after looking at the fence where you're trying to setup the jump and try jumping across and use your revolvers to slow yourself in mid air as your standing on the barbwire. If done successfully you will be hovering over the barb wire for a bit and fall into a section of it that has no collision. It is very important you save here as sometimes even the slightest movement can push you off the fence. Go back into first person for the next jump across to the next part of the fence in order to stop your forward momentum and land there successfully. Save again when you make it and jump the next gap in first person to stop your forward momentum and precisely move across the fence. Save again once you make that and then you have to move as far back on this fence as possible to be able to get forward momentum to jump on the basketball hoop and then jump on the siren. Jump on the top after that and then the wall you need for the sequence break, save and then slowly fall down the part of the wall that has the door in 1st person and spam the action to open the door to skip several levels.