In part I (here) I laid out how chops concerns in many respects drive proper use of an assistant, especially at a professional level. That is why you need to use an assistant. Now it is time to turn to the topic of how to use an assistant, with some professional examples.
An aside: Some pros don’t mark the part at all
My Doctoral studies were under Michael Hatfield at Indiana University. He had been Principal Horn in Cincinnati for many years and told me that in Cincinnati he did not put any markings in his parts! The system was that the assistant just came in and played any time he felt that he should. If you played together all the time in a group, this system might actually work fine, but I don’t suggest it as ideal, I think you should make some markings and have a system.
Introducing Tom McAninch
I don’t know the exact years he served as Principal Horn, but Tom McAninch (1953-2019) was a former Principal Hornist of the Nashville Symphony by the time I arrived (as Third Horn) in 1991. At that time, he was one of two full time studio horn players (along with Eberhard Ramm, another former Principal Hornist), and I played with him many times. Tom was from a musical family (his father was for some years principal oboe of the Louisville Orchestra), and he was a Curtis graduate, with additional studies with Farkas. Tom passed (too young) from ALS. When I knew him, he was heavily into body building.
One summer in the later 1990s I was playing a particularly badly orchestrated gospel session with him. We got to the lunch break, he called a sub and said something like “this is my career,” and he quit playing horn. Reached his limit of bad orchestrations that day; focused going forward on copy work and piano tuning. Maybe a year after that he had a sale of all his horn music, and I bought a good bit of it, including his copy of the book of Strauss first horn parts, published by Wind Music.
What was great about the book was he was a fastidious record keeper and performed three of the works in the Nashville Symphony from that book, with all the markings documented there for potential future reference. They are not quite as I would do them, but extremely interesting to look at as a model for what you might do.
Professional markings look like this
As Tom was a Curtis grad, I’d like to think he was influenced by the Horner school of assistant markings. I see lots of logic to his markings; they are worth a closer look as examples.
Don Juan
His markings on Don Juan are a great place to start. To begin, we have the top of page 1. The assistant plays the passages inside the brackets, and clearly, they could triple tongue and carry the first part on a high level.

I wonder if the assistant used a stop mute for the note before C? In any case, they could get set up well for the note.
The top of the first page being done as it was leaves plenty of chops to feel good about the bottom of the page. Tom plays most of this passage, but with the assistant dovetailing in on two specific notes.

Check out also the alternate fingerings. Write them in! It’s OK to do that.
The whole part may be found from the links at the end of this article. I’d like to close out this look at Don Juan with the end of the piece. The last page is a bit of a blow, and you can see that Tom used the assistant a good bit, splitting things close to half and half. This left him relatively fresh for those two pp passages on the last line, notes you’d like to be fresh for.

Ein Heldenleben
As a side point, I’ve actually played (at Brevard) principal horn on Don Juan and Heldenleben on the same concert! For Heldenleben you very much need a good assistant.
Tom uses the assistant twice in the opening, which you might never have considered doing. We work on the opening as an excerpt, but if you are playing the piece on a concert, you can approach it differently. In his case, I’m wondering if he did not feel secure with the very opening passage? Or maybe the assistant had great low flexibility? The use of the assistant in the second line also solves a breathing problem.

This big passage later in the work, on first glance it would look like Tom is laying out at 78, but actually I believe (based on the breath marks) that he is doubling with the assistant for much/most of it. But 3 before 79 they had a specific plan for Tom to play for sure that note. In any case, he would be saving chops some here, depending how he felt, to be relatively fresh for the soloistic passages at 81.

Finally, the end of the work. By now your chops are toward the end of what you can do, and to have an assistant that you can split the part with is so helpful. The passage is very delicate. You might think it is overkill in a way for the assistant to play so much, but you do need to have something left for the last note when it finally comes.

The full parts
These markings are worth your study as an aspiring principal horn. Make use of the general principals you see, they will help you out. For a complete look at his part for both pieces see the PDFs linked below.
Heldenleben-horn-1-assist-marked
Update: For a podcast on the topic see Episode 67 of the Horn Notes Podcast (direct link, but find it anywhere you get podcasts).

