How do I use SharpSVN to programatically to add a folder to the ignore list?

EDIT: Attempted:
Here's what I've tried

svnClient.GetProperty(new SvnUriTarget("svn://svn.foo.com/" + DatabaseName + "/"), SvnPropertyNames.SvnIgnore, out ignores);
ignores += " Artifacts";
var args = new SvnSetPropertyArgs() { BaseRevision = ???, LogMessage = "update ignore list" };
svnClient.SetProperty(new Uri("svn://svn.foo.com/" + DatabaseName + "/"), SvnPropertyNames.SvnIgnore, ignores, args);

But I don't know how to get the BaseRevision (I can get it manually, and that works, but all the combinations of GetProperty I tried don't seem to give it to me.)

SOLUTION: Based on Bert's Answer

SvnGetPropertyArgs getArgs = new SvnGetPropertyArgs(){};
string ignores = "Artifacts";
string result;
if(svnClient.GetProperty(new SvnUriTarget("svn://svn.foo.com/" + ProjectName + "/trunk/"), SvnPropertyNames.SvnIgnore,out result))
{
    ignores = result + " Artifacts"; //TODO: check for existing & tidy formatting.
}
svnClient.SetProperty(UncPath.TrimEnd('\\'), SvnPropertyNames.SvnIgnore, ignores);
SvnCommit(svnClient);