Let's start off with saying that there is no cure for this. You (and your plants) just have to learn to live with it as best you can. Sorry.
What is Crown Gall?
There are many types of gall, with many varied causes. And they are not confined to just roses. You will see galls on my types of trees, from Apples to Oak. Some are caused by damage to the plant, some by insects, some by virus, and some by fungi. Crown Gall is caused by the bacteria Agrobacterium, which may be present in the soil. It can get infect the plant by entering via damage caused by poor pruning, wind rubbing crossed stems, animal damage and so on.
The main way to avoid crown gall, is to try and minimize damage caused to the plants. So when you are pruning, use good quality sharp tools. Major pruning cuts can be treated with sealant (white glue or PVA glue is as good as anything) and this can also help with cane borer as well. Other than that, it just comes down to luck as much as anything.
Sorry, but once Crown Gall is established in the plant there is nothing you can do to cure it. As the gall gets bigger it can dry out and become crumbly, and you might be able to dilodge the majority of it. However, it will grow back sooner or later. While the gall can sap some of the vigor from you plant, and it may become more prone to stress if it gets too dry, it can probably survive quite well for many years to come.
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