Snails, not slugs
Please send one or several full-size images of the snails when you reply to this email. After we identify them, I can suggest a suitable management plan.
Thank you for sending the images which clearly show brown garden snails, Cornu aspersum (formerly Helix aspersa). Some portions of Multnomah County are heavily infested with them
Judging by the snails' size, they have been around much longer than just this year. If they had hatched this spring, they would be a scant 1/4-inch in diameter. During their 4-year lifespan, they grow to about an inch in diameter.
The truly bad news is that you're unlikely to get rid of these snails. Even if you could, others would move in from next door. As said above, they are well-established here and there in the Willamette Valley.
To limit the snails’ destructive dining activity will require vigilance on your part, combined with instant action when you see one or more. On-the-spot tactics include stomp them; drown in soapy water; or crush. Longer term, you can also trap them and/or use appropriate snail baits. A combination program is more effective than using only one technique.
This information from the University of California contains further details: "Snails and Slugs" http://ipm.ucanr.edu/PMG/PESTNOTES/pn7427.html