WPF interaction command refer to local static resource for converter

I wish to create a "reusable" control item which has a behaviour attribute. As described in this blog

For the data binding the data has to be converted. The problem is; as StaticResource it can only see the top level dictionary (app), and dynamic resources don't work ("can only be used with a dependency property").

The simple (working) xaml (window):

<Window x:Class="testit.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"        
        xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Rectangle x:Name="blah" Fill="Yellow" Stroke="Black" Width="100" Height="100">
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="MouseEnter" >
                    <i:InvokeCommandAction Command="{Binding MouseEnterCommand}">
                        <i:InvokeCommandAction.CommandParameter>
                            <Binding Path="Name"
                                     Converter="{StaticResource SelectionConverter}"
                                     RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType=Rectangle}" />
                        </i:InvokeCommandAction.CommandParameter>
                    </i:InvokeCommandAction>
                </i:EventTrigger>
            </i:Interaction.Triggers>
        </Rectangle>
        <TextBlock x:Name="namefield" Text="{Binding Data}" HorizontalAlignment="Left" VerticalAlignment="Top"/>
    </Grid>
</Window>

app:

<Application x:Class="testit.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:testit"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <local:SelectionConverter x:Key="SelectionConverter" />
    </Application.Resources>
</Application>

And finally the viewmodel:

using System;
using System.ComponentModel;
using System.Globalization;
using System.Windows.Data;

namespace testit
{
    class ViewModel : INotifyPropertyChanged
    {
        private string _data;
        private readonly DelegateCommand<string> _mouseEnterCommand = null;

        public ViewModel() {
            _data = "hello ";
            _mouseEnterCommand = new DelegateCommand<string>(
                (s) => {
                    var a = s ?? "world ";
                    Data += s;
                    return;
                });
        }

        public DelegateCommand<string> MouseEnterCommand => _mouseEnterCommand;

        public string Data {
            get { return _data; }
            set {
                if (value == _data) return;
                _data = value;
                OnPropertyChanged("Data");
            }
        }


        public event PropertyChangedEventHandler PropertyChanged;
        protected virtual void OnPropertyChanged(string propertyName) {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }
    public class SelectionConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
            if (value == null) return "";
            char[] charArray = ((string)value).ToCharArray();
            Array.Reverse(charArray);
            return new string(charArray);
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
            throw new NotImplementedException();
        }
    }
}

Now as said, this "works". However it doesn't do what I wish: it clutters the top level resource dictionary. I wish to remove the resource from app. and put it under the Grid. (Or whatever panel I use).

<Grid.Resources>
    <local:SelectionConverter x:Key="SelectionConverter" />
</Grid.Resources>

EDIT:If I add above line to the grid inside the window the following error is thrown on compilation (the line and position refer to the Converter="{StaticResource SelectionConverter}")

"'Provide value on 'System.Windows.StaticResourceExtension' threw an exception.' Line number '13' and line position '38'."

With the inner exception:

Cannot find resource named 'SelectionConverter'. Resource names are case sensitive.

For clarity, this is the modified window.xaml:

<Window x:Class="testit.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"        
        xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
        xmlns:local="clr-namespace:testit"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Rectangle x:Name="blah" Fill="Yellow" Stroke="Black" Width="100" Height="100">
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="MouseEnter" >
                    <i:InvokeCommandAction Command="{Binding MouseEnterCommand}">
                        <i:InvokeCommandAction.CommandParameter>
                            <Binding Path="Name"
                                     Converter="{StaticResource SelectionConverter}"
                                     RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType=Rectangle}" />
                        </i:InvokeCommandAction.CommandParameter>
                    </i:InvokeCommandAction>
                </i:EventTrigger>
            </i:Interaction.Triggers>
        </Rectangle>
        <TextBlock x:Name="namefield" Text="{Binding Data}" HorizontalAlignment="Left" VerticalAlignment="Top"/>
        <Grid.Resources>
            <local:SelectionConverter x:Key="SelectionConverter" />
        </Grid.Resources>
    </Grid>
</Window>