Hi Collin, good question.
There is not a straightforward rule to differentiating between adjectives and verbs. For example, you wanted to differentiate using “-ing”, but unfortunately that’s not a universal rule to identifying verbs.
How I would think about it is to go back to the definition of what a verb and an adjective is.
Verb – a word used to describe an action, state, or occurrence, and forming the main part of the predicate of a sentence, such as hear, become, happen
Adjective – word naming an attribute of a noun, such as sweet, red, or technical
The above definitions can be found on google, but intuitively, you can think about a verb as a word describing an action (eating, running, doodling, studying, writing, etc.), whilst adjectives are used to describe a noun.
The confusing part occurs when verbs are used as adjectives. For example, the ticking clock. “ticking” could be used as an adjective or a verb. As a verb, it would be “I could hear the clock ticking”.
Verbs are used as adjectives, when the action is being done “all or most” of the time.
I hope the above helps you in your understanding of the differences.
All the best, and the best advice to differentiating it is to read more. Intuition in language can be quite helpful. 🙂