I wish I had some good news for you, but here are the facts: deer will eventually get used to anything if they are hungry enough or like a plant enough. All the products saying they will keep deer away are going to be, at best, temporary. 'Jetting' sprinklers can be somewhat effective, but unless they are motion activated you can lose a lot of money.
You can net the trees like many pros do - I believe the netting is available through many garden supply companies. You may anger some birders, though, as birds can get caught up in the netting.
The most effective deterrent and the most expensive... a very high fence. We're talking twelve feet. Deer can jump quite high when determined.
I always hated giving customers the 'low down' on deer because there's just no easy, inexpensive answer. The very callous response from some people is to hunt them and thin the population so that the native flora is enough to satisfy them. Unfortunately, it's a valid point.
Best to you,
Ging

Motion activated 'Jetting' sprinklers work well for me in my 1/2 acre + garden. But you have to have enough to cover the area that you want to protect.

I started with one and it worked well for a while. Then they started to approach from the other side and ate everything outside of the range of the sprinklers motion detector.

I added another and they figured out that they can come from the sides. I have bought two more for this year one for each corner.

You also have to check often and make sure that the batteries are good because they seem to test it every night or so. One night with a dead battery can mean losing everything.

Also, sometimes a very small deer may be able to go undetected and do a lot of damage. But if you make the settings sensitive enough to set them off with a small deer the wind blowing leaves and stuff will set it off also and waste water.

Found something fascinating. At West Virginia Botanical Gardens they have been using diluted milk to deter deer feeding on their plants with great success. The ratio is one to three (milk to water) but it's important to read the article because there can be danger from using too much. Really interesting, though; it would be worth trying in my opinion because this is about as close as you can come to an experiment from an expert with positive results. The link actually takes you to an article that has the info to get to the original article at Horticulture magazine's website.
Maybe this would be an option.
Ging

Here is a link that might be useful: Milk as deer repellent

We put up (temporary) 6 ft fencing around the base of our cherry tree last year, just about one foot beyond the edge of the outer branches. We only need it up during spring as the tree is just leaving out, after that the deer don't seem to bother the tree.