I had the problem with the frogs getting to the back part of the filter where your pump would be, I have an external pump so the pipe that draws water for the pump is in this area so similar to yours. What I found is that the frogs were able to that area where the handle is for the skimmer basket. I just use a sponge and put it there to keep the frog from being able to get to that area. I pull one out this time of year daily, they seem to like it in there for some reason, they hide under the skimmer door. I saw your photo and what it looks like is that the frogs and salamanders are climbing over the net and into the pump area. You need to block this part off with a screen of some sort like RobAmy said, but would need to modify it for your particular skimmer. I think you will have to choose whether you want to collect the leaves or keep the salamanders out as I don't think you can put rods in front and still collect leaves or keep the salamanders out. You would have to put the rods so close together that it would defeat the purpose of the skimmer. Something else you could try is what I do in the fall when the leaves are falling like crazy and I can't check my skimmer every hour to empty. I made a "net" for in front of my skimmer to collect the leaves and still allow enough water flow through to keep the pump pumping and the waterfall flowing. Then every night I would go out and empty all the leaves from this net. I had to do this as I don't cover my pond in the fall and this helps eliminate the problem of clogging my skimmer with too many leaves.