Sorry about the damage to your heptacodium Pat. Milorganite, and I have never used it just seen it and read about it, is an organic type fertilizer produced from sewer sludge and as such the nitrogen shouldn't be a fast release so shouldn't be an issue with your clematis. As to whether that will keep rabbits or whatever might be doing the damage away from your plants, I don't know if that is one of its attributes or not. Typically for those clematis that I have issues with rabbits biting the stems, I have simply made cages out of plastic or metal fencing that are about 1 to 2 feet tall and caged the clematis to keep the rabbits away from the stems.

Here is an example of such a clematis protected.
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Miguel, I was afraid you or someone would say I needed to cage! I've always gotten away without caging or indeed any sort of animal protection. But apparently that won't happen this year. Do you take the cages off at some point in the summer?

I personally don't take them off but it may be that later in the summer there are other things to eat and they won't bother the clematis. Besides that I am way too lazy to put them up and then take them down only to put them back up again! LOL

Ah, but you have a mature, lush garden where cages don't show. I'm not there yet. I just deposited little piles of milorganite all around the garden, especially near the clematises, daylilies, fothergilla, serviceberry, and heptacodium. We'll see what happens. While I was wandering around, I found two of my more mature clematises already putting out buds all over the place, so I pruned them. Nothing else is ready yet, but I guess it's time for the daily walk with pruners -- a little early this year.