I hope this message finds you well, present circumstances excluded. As you likely know, unless prohibited by contract, the landlord does have the right to make you remove the barriers under law.
That being said, you also have the right to quiet enjoy of your property without the nuisance and health hazard of animals defecating on your leased premises.
The link is to the Washington State Landlord Tenant Laws...in particular, the duties of the landlord: http://apps.leg.wa.gov/RCW/default.aspx?cite=59.18.060
Notice, Subsection (4). It states: (4) Provide a reasonable program for the control of infestation by insects, rodents, and other pests at the initiation of the tenancy and, except in the case of a single-family residence, control infestation during tenancy except where such infestation is caused by the tenant;
Unless you are doing something to cause the infestation of the raccoons, then it is the responsibility of the landlord to make accommodations to fix the problem.
This is the law on the notice you are to give the landlord to correct the condition: http://apps.leg.wa.gov/RCW/default.aspx?cite=59.18.070
This is the law on the failure to remedy the condition: http://apps.leg.wa.gov/RCW/default.aspx?cite=59.18.090
This is the law on the ability to get reduced rent as a result of the landlord failures:
I suggest you print off these laws and show them to the landlord...give the landlord copies of the laws. You then respectfully XXXXX XXXXX the problem be solved or you will be forced to take the necessary legal action.
To answer your question directly, the landlord's responsibility is to remedy the problem or take all reasonable actions to remedy the problem. If he does not, you have a case for reduced rent as we result.
Let me know if you have any additional questions or comments.
Best wishes going forward.