The blacktail deer belong to the state of Washington unless you have purchased them and are running a game farm.  If you have people coming onto your property without your permission to hunt them then there are a couple of things that you can do.  The first is to make sure that you have it posted "No Trespassing" and or "No Hunting" properly.  Then if you see a person on your property you can get the sheriff involved to deal with the trespassers.  The best thing to do is to check with your local government or the Washington Department of Fish and Game http://wdfw.wa.gov/ and see just what your options are. 

While asking a question like this on a open forum will get you a lot of answers not all of them would be legal for you to do.   

Critter is absolutly correct, The deer belong to the state of washington(tax payers). If people are tresspassing on your property there are a few things to do. like Crittter said the property has to posted "no tresspassing" and or "no hunting". In oregon the signs need to be every 150' i think and the signs must be 12"x12". if the property is not posted properly then unfortunitly any joes shmoe can come on your land without getting into trouble. the worst that will happen is you'll can the police and they'll ask the perp to leave. also like critter said look at the wash fish and wildlife website for washingtons exact laws for posting your property as all are a little different. and as far as a wildlife farm, you need a permit and they are VERY hard to come by. in oregon they only give out a very few permits and its almost impossible to get. if they are all filled up you have to wait till a farm give there permit back to the state.

here in kansas. private property boundaries are painted with purple paint. that way, everything that's off limit to hunters is clearly and definately marked. we call it the purple plague here. but if you are a property owner, it's your right to restrict access.

here in kansas though, purple generally means, don't even ask for permission to hunt.

that's kind of sad. but it's life.

the safest thing to do is not necessarily confront the tresspasser, but to post your property