What is the best method for checking if a file exists from a SQL Server 2005 stored procedure?

using System;
using System.Data;
using System.Data.SqlClient;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Server;
using System.Security.Principal;

public partial class StoredProcedures
{
    [Microsoft.SqlServer.Server.SqlProcedure]
    public static void FileExists(SqlString fileName, out SqlInt32 returnValue)
    {
        WindowsImpersonationContext originalContext = null;

        try
        {
            WindowsIdentity callerIdentity = SqlContext.WindowsIdentity;
            originalContext = callerIdentity.Impersonate();

            if (System.IO.File.Exists(Convert.ToString(fileName)))
            {
                returnValue = 1;
            }
            else
            {
                returnValue = 0;
            }
        }
        catch (Exception)
        {
            returnValue = -1;
        }
        finally
        {
            if (originalContext != null)
            {
                originalContext.Undo();
            }
        }
    }
}

USE master
GO
CREATE ASYMMETRIC KEY FileUtilitiesKey FROM EXECUTABLE FILE = 'J:FileUtilities.dll'
CREATE LOGIN CLRLogin FROM ASYMMETRIC KEY FileUtilitiesKey
GRANT EXTERNAL ACCESS ASSEMBLY TO CLRLogin
ALTER DATABASE database SET TRUSTWORTHY ON;

DECLARE @i INT
--EXEC FileExists '\\server\share\folder\file.dat', @i OUT
EXEC FileExists 'j:\file.dat', @i OUT
SELECT @i