Public Class Form1

    Private Sub moveSentry()
        If sentry.Tag = "down" Then
            sentry.Location = New Point(sentry.Location.X, sentry.Location.Y + 2)
        End If
        If sentry.Tag = "up" Then
            sentry.Location = New Point(sentry.Location.X, sentry.Location.Y - 2)
        End If
        If sentry.Tag = "right" Then
            sentry.Location = New Point(sentry.Location.X + 2, sentry.Location.Y)
        End If
        If sentry.Tag = "left" Then
            sentry.Location = New Point(sentry.Location.X - 2, sentry.Location.Y)
        End If
    End Sub
    Private Sub checkCorners()
        If sentry.Location.X = 0 And sentry.Location.Y = 0 Then
            sentry.Tag = "down"
            sentry.Image = Image.FromFile("down1.png")
        End If

        If sentry.Location.X = 0 And sentry.Location.Y = 202 Then
            sentry.Tag = "right"
            sentry.Image = Image.FromFile("right1.png")
        End If

        If sentry.Location.X = 218 And sentry.Location.Y = 202 Then
            sentry.Tag = "up"
            sentry.Image = Image.FromFile("up1.png")
        End If

        If sentry.Location.X = 218 And sentry.Location.Y = 0 Then
            sentry.Tag = "left"
            sentry.Image = Image.FromFile("left1.png")
        End If

    End Sub
    Private Sub sentryTimer_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles sentryTimer.Tick
        moveSentry()
        checkCorners()
    End Sub
End Class