USE test;
GO
CREATE TABLE LogonAudit
(
    AuditID INT NOT NULL CONSTRAINT PK_LogonAudit_AuditID
                PRIMARY KEY CLUSTERED IDENTITY(1,1)
    , UserName NVARCHAR(255)
    , LogonDate DATETIME
    , spid INT NOT NULL
);
GO
GRANT INSERT ON Test.dbo.LogonAudit TO public;
GO
CREATE TRIGGER MyLogonTrigger ON ALL SERVER FOR LOGON
AS
BEGIN
    IF SUSER_SNAME() <> 'sa'
    INSERT INTO Test.dbo.LogonAudit (UserName, LogonDate, spid)
            VALUES (SUSER_SNAME(), GETDATE(), @@SPID);
END;
GO
ENABLE TRIGGER MyLogonTrigger ON ALL SERVER;

CREATE TRIGGER MyLogonTrigger ON ALL SERVER FOR LOGON
AS
BEGIN
    IF SUSER_SNAME() = 'SomeUser'
    INSERT INTO Test.dbo.LogonAudit (UserName, LogonDate, spid)
            VALUES (SUSER_SNAME(), GETDATE(), @@SPID);
END;