Roy G Biv
Senior Member
Most established trees can deal urine w/o issue. Smaller trees w/less developed root systems will get into trouble. Even 1-year of root growth diminishes the risk of mortality substantially.
As such you don't necessarily need to cage landscapes areas off indefinitely, but temporary, if sturdy fences can be useful.
There are also non-fence barriers that can be used. These could include smells that would offend a dog and discourage it from being in proximity to said plants; you don't need high concentrations given dogs relatively better sense of smell.
Even little fences around the base of each tree would do. Just need to keep the urine out of the critical root zone. I doubt you need to fence out to the boundary of the drip zone.